Forensic Sci Med Pathol

DOI 10.1007/s12024-010-9198-1

CONTINUING MEDICAL EDUCATION REVIEW

Blood stain pattern analysis

O. Peschel S. N. Kunz M. A. Rothschild
E. Mutzel

Accepted: 23 September 2010

 Springer Science+Business Media, LLC 2010

Abstract Bloodstain pattern analysis (BPA) refers to the

collection, categorization and interpretation of the shape
and distribution of bloodstains connected with a crime.
These kinds of stains occur in a considerable proportion of
homicide cases. They offer extensive information and are
an important part of a functional, medically and scientifically based reconstruction of a crime. The following groups
of patterns can essentially be distinguished: dripped and
splashed blood, projected blood, impact patterns, cast-off
stains, expirated and transferred bloodstains. A highly
qualified analysis can help to estimate facts concerning
the location, quality and intensity of an external force. A
sequence of events may be recognized, and detailed
questions connected with the reconstruction of the crime
might be answered. In some cases, BPA helps to distinguish between accident, homicide and suicide or to identify
bloodstains originating from a perpetrator. BPA is based on
systematic training, a visit to the crime scene or alternatively good photographic documentation, and an understanding and knowledge of autopsy findings or statements
made by the perpetrator and/or victim. A BPA working
group has been established within the German Society of
Legal Medicine aiming to put the knowledge and practical
applications of this subdiscipline of forensic science on a
wider basis.

O. Peschel  S. N. Kunz (&)  E. Mutzel

Institute of Legal Medicine, Ludwig Maximilians University
of Munich, Nussbaumstr. 26, 80336 Munich, Germany
e-mail: sebastian.kunz@med.uni-muenchen.de
M. A. Rothschild
Institute of Legal Medicine, University of Cologne, Cologne,
Germany

Keywords Bloodstain pattern analysis  Homicide 

Crime scene analysis  Crime reconstruction  Forensic
science

Bloodstain pattern analysis (BPA) is the examination of

shapes and the categorization and distribution of bloodstain
patterns in order to provide an interpretation of the physical
events of a crime which gave rise to their origin. The
bloodstain patterns can give valuable information concerning the events which lead to their creation when
examined by a qualified analyst. The information gained
can then be used for the reconstruction of an incident and
the evaluation of statements of witnesses and crime participants. BPA is an important forensic method in addition
to autopsies, basic crime scene work, and molecular biology. The genetic examination especially is an essential part
and an important requirement for a solid analysis of
bloodstain patterns. The use of these scientific methods,
physical evidence, deductive reasoning, and their interrelationships are the main keys to gaining explicit knowledge
of the series of events that surround the commission of a
crime.
The first systematic examinations of blood shapes and
distribution were done by Piotrowski in 1895. Schmidtmann discussed in 1905 the possibilities of crime reconstruction with the help of morphologic analysis of blood
stains. Further investigations on this matter were done by
Ziehmke in 1914, among others, considering the distinctive
morphological features of blood patterns depending on
the height of the fall. Balthazard and colleagues (1939)
published findings about reconstructing the angle of impact
from the impact pattern by measuring the width and length
of small blood stains. Additional studies about expiration
pattern were done by Mueller and Schleyer (1975) and in

Forensic Sci Med Pathol

more recent years by Brinkmann, Rand and Karger [13].

An historic overview can be found in the publications of
Brinkmann [1] and significant American textbooks, especially by MacDonell [4], James [5] and by Bevel and
Gardner [6].
However, the essential basic knowledge of the applied
bloodstain pattern analysis on the crime scene is mainly
evidence based and relies on experience. A detailed systematic differentiation and documentation of various
bloodstains and their origin on the crime scene is fundamental for reliable subsequent interpretations. There are
existing computer-based programs offering a specific
documentation and analysis of bloodstain patterns, but they
have not already been integrated in routine crime scene
work due to practical problems.
In the USA the International Association of Bloodstain
Pattern Analysts (IABPA) was found in 1983 and the
German working group was established within the
Deutsche Gesellschaft fur Rechtsmedizin in 2005.

Biophysical fundamentals
Blood, a specialized colloidal bodily fluid within the circulatory system, is a complex composition of blood cells
and plasma. Blood accounts for approximately 8% of the
body weight, with an average density of approximately
1,060 kg/m3. The average adult has from about 45 l
(female) and up to 56 l (male) of blood.
As with any other liquid, blood is defined as a substance
with no shape of its own, adjusting to its surrounding. It has
certain physical characteristics which are essential for its
morphological interpretation:

specific weight,
viscosity,
and surface tension.

Any other biological features of blood considering its

cellular components and biochemical consistence are of
minor importance in blood stain analysis and will therefore
not be discussed any further.
The dynamic viscosity g of blood is a measure of the
internal resistance of blood to flow, which is being
deformed by either shear stress or extensional stress. The
SI physical unit of dynamic viscosity is the pascal-second
(Pa s), which is equivalent to kg m-1 s-1. This means, that
if a fluid with a dynamic viscosity of one Pa s is placed
between two plates, and one plate is moved aside with a
shear stress of 1 Pa, it overcomes a distance, which is equal
to the thickness of the layer between the plates in 1 s.
MacDonell has examined this and, depending on surrounding temperature, come to the result that the viscosity
of blood equals 1.62.5 mPas (37C) resp. 3.44.3 mPa s

(25C). As a comparison, other sources published figures

between 4 and 25 mPa s considering water: 1, petroleum:
0.65, ethanol: 1.19, glycerin: 1,480 and paraffin: 102106.
Even though blood viscosity also depends on individually
varying hematocrit and coagulation, no reports have been
published stating relevant differences in interpretation of
bloodstain patterns.
Adhesion is the tendency of certain contrasting molecules to become attached to each other due to attractive
forces. This relatively strong cohesion is especially
important on surfaces allowing a very good material
transmission from one object to another. (A little blood
can go a long way in contaminating everything with which
it comes into contact [6] p. 108).
Cohesion is the tendency of certain comparable molecules to become attached to each other because of
attractive forces. For instance, a drop of blood is affixed
to solid material such as a wall or a knife by adhesive
forces.
Surface tension is the elastic like property of a fluid
created by cohesive forces between liquid molecules. It is
measured in the dimension of force per unit length or
energy per unit area. Surface tension of blood varies with
altering temperature and can measure between 27 and
34 mN/m at 37C and up to 4958 mN/m at 25C, compared with water, which results in approximately 73 nM/m
at 20C or ethanol (approx. 23 nM/m at 20C).
All liquids have the tendency to reduce their surface as
much as possible. Provided that no other forces are
involved, a drop of blood has a round, circular shape and
not, as often presented the outline of a tear.
Before blood leaks from a wound or body surface, mass
and gravity of the forming droplet has to overcome the
surface tension of the fluid. This means that under ideal
statical circumstances, identical and reproducible droplets
of 50 ll can be created. This standardized droplet has been
described by MacDonell as the typical droplet [4]. This
definition is debatable, especially since the size of a droplet
is highly dependent on the structure and type of the surface
from which it evolves.
Oscillation describes the small movements of a drop of
liquid when falling, causing a shift of the droplets outline
from a perfect sphere to an elongate spheroid. The cohesive
forces of surface tension are responsible for the spherical
shape of a drop of blood, whereas the retention of this
spherical shape is due to the viscosity of blood. When
falling, these forces are influenced by gravity, air resistance
and the movement of the molecules within the dropping
blood, leading to its fluctuation in shape. This oscillation is
the reason for the stability of a droplet, preventing its
separation into various parts when falling.
MacDonell found that small droplets (1 mm in diameter
and less) were almost perfect spheres, whereas larger drops

Forensic Sci Med Pathol

were unable to maintain a sphere shape in flight [7]. The

width-and-length-determinations of the resulting bloodstains can then be used to detect the acute angle formed
between the direction of a blood drop and the plane of the
surface it strikes (=angle of impact).
When blood is being influenced by variable exterior
forces, smaller droplets can be created, which themselves
are then exposed to outer physical forces such as air
resistance and gravity. The higher the effective energy, the
more likely it is that the surface tension is destroyed and
the smaller are the resulting droplets. This leads to the
conclusion that blood droplets in the dimensions between
0.125 and 2 mm and with a capacity from 0.008 ll up to
4 ll will be expelled from the impact site if the human
body is hit with a sufficient force. The size, shape and
number of resulting stains primarily depend on the amount
of force utilized to strike the blood source, but they normally dont extend 45 mm in diameter (with droplets of
up to 2 mm).
Air resistance affects forces that oppose the relative
motion of an object through gas.
When the droplet initially breaks free, it is very slightly
elongated. Then, due to air resistance its sphere starts to
flatten a little, but still maintains its stability. The resulting
shape is a ball or sphere, exposing the least amount of
surface area possible. This differs from the typical media
representation of a teardrop shape of a falling drop of
liquid.
Because of the fact that smaller droplets have a minor
volumesurface ratio than bigger droplets they are more
influenced by air resistance. This especially applies when
their movement is not entirely vertical, but has a slight
horizontal component. The air resistance is in inverse
proportion to the size of the drop of blood with the consequence that larger drops can cover a longer distance than
smaller ones. This effect is essential when blood has been
reduced to a fine spray, as a result of high energy applied to
it, e.g. in combination with a gunshot wound. The maximal
distance where this phenomenon can normally occur is not
more than 120 cm.
When a flying drop of blood hits a surface four phases of
impact can be differentiated: contact, shifting, dispersion,
retraction.
Contact is made when free falling drops interact with a
surface. On impact their original spherical form collapses.
In the phase of shifting, the spherical outline of the
droplet is destroyed and the main mass moves radial outwards (angle of impact 90), leaving the surface tension
still intact. At the outer ring of the droplet a small overlap
might occur, which then leaves a larger bloodstain than the
original droplet. A 4 mm droplet could therefore create up
to an 8 mm large bloodstain. Depending on the oscillation
phase of the droplet a variation of the length-to width-ratio

is also possible. Pointed edge characteristics that radiate

away from the center of a bloodstain (so called spines) are
common side effects of the shifting phenomenon, especially when the angle of impact is rather low (Fig. 1).
The shifting process is influenced by rough surfaces,
which cause irregular uneven stains and even fine satellite
stains. The greater the height from which a droplet falls, the
more this side effect can be seen.
Dispersion describes the mass movement of the margin
against the main original direction of the whole droplet.
While shifting is a lateral motion, dispersion can be seen as
an upright (reverse) movement. The droplets stability is
maintained because of the cohesive forces of the surface
tension.
The phase of retraction is the last moment of the creation of the bloodstain, when all exterior forces have been
reduced and the surface tension remains.
A blood drop that strikes a fluid (blood) causes an
accentuation of the dispersion phase with clear satellite
spatters, which sometimes can be arranged asymmetrical.
MacDonell describes the typical blood droplet as a
droplet with 50 ll in volume and approximately 4.6 mm in
diameter. Such a droplet reaches its terminal velocity of
89 m/s at a height of fall of 69 m. Smaller droplets with up
to 1 mm in diameter and a volume of about 0.61.2 ll reach
lower terminal velocities of approximately 2.53.5 m/s at a
height of fall of approximately 50100 cm.

Fig. 1 Pointed edge characteristics, so called spines

Forensic Sci Med Pathol

Target surface texture

The type of surface blood strikes has an affect on the
resulting spatter, including the size and appearance of the
blood drops. Different kinds of surfaces have an influence
on the four phases of impact of a droplet and therefore on
the resultant shape. In general it can be said that the
smoother, harder and less porous a surface, the minor is the
distortion (scalloping) around the edges (Fig. 2). The reason for this is the rather high surface tension, which can be
easier overcome than when an irregular subsurface or
porous surface is hit. Because of this, conclusions considering the height from where a blood spatter occurred are
rather difficult and can, if necessary, only be reconstructed
on the actual object in question.
In order to interpret a blood stain, the targets surface
texture, the form of each individual droplet as well as its
size, distribution and the situation itself have to be taken
into account.

Passive drop
Transfer/contact pattern
Projected bloodstains

Passive drop (bleeding) is a flow pattern or bloodstain

drop(s) caused or formed by the force of gravity acting
alone: blood clot, drip stain, flow stain, blood pool, serum
stain.
Transfer/contact pattern is a bloodstain pattern created
when a wet, bloody surface comes in contact with a second
surface. The original surface may be observed within the
pattern, as a whole or as a recognizable image: contact
pattern, wipe pattern (primary and secondary), insect stain
(fly spots).
Projected bloodstains are created when a blood source is
exposed to a force greater than the force of gravity: arterial
spurting pattern, cast-off pattern, spatter stain, expiration
pattern, spine pattern, void pattern, perimeter stain.

Passive drop
Recommended terminology
The shape and pattern of blood drops can reveal important
information about the nature of the wound from which the
blood originated. Depending on the injury certain bloodstain patterns can be differentiated by their unique geometrical characteristics. In order to maintain an objective
view it is necessary to have a specific, unique way of
describing bloodstain patterns, so that, when reading a
blood stain pattern analysis report, any specialist is able to
understand the mechanisms behind each pattern. A standardized scientific approach of blood stain pattern interpretation has been defined by The Scientific Working
Group on Bloodstain Pattern Analysis (SWGSTAIN) [8],
which mainly complies the terminology used by the
German Arbeitsgruppe fur BlutspurenVerteilungsanalyse.
Using this terminology three basic categories can be
differentiated:

Fig. 2 Fall from 50 cm. a On cotton. b On a tile. c On wood

Blood clot or thrombus describes the final product of blood

coagulation. When vessels are damaged, platelets within
the blood are activated, starting the coagulation cascade
leading to a 3-dimensional pattern of jelly-like clotted
blood. This is often related with a serum stain, a segregation of clear, cell-free blood which wont coagulate. Patterns like these can be found as a direct consequence of
passive flow pattern on inhomogeneous surfaces, which
have a rather high resistance (carpet floors, tar, etc.).
A drip stain is a droplet falling through air without any
disturbance. It will physically hold on to its spherical shape
without breaking into smaller droplets. Such a blood drop
may descend from an exposed wound or any object containing a sufficient amount of blood to permit the formation
of a drop. Bloodstains caused by spherical free-falling
blood are circular in shape when landing on a smooth
homogeneous surface (Fig. 3). Depending on the volume

Forensic Sci Med Pathol

Fig. 4 Fall from 50 cm with an impact angle of 10

of the drop, the distance fallen and the surface texture it

lands on, the shape and size of the droplet varies. Due to
different variables it is very difficult to reconstruct the
exact height and volume of a droplet just by analyzing its
pattern. It is, however, possible to calculate the angle of
impact by examining the length and width of a resulting
drip stain. This specific angle is the internal angle formed
between the flight path of that drop and the target surface it
strikes (Graph 1).
Angle of impact arc sin w=l
A blood drop hitting a rather smooth horizontal surface
in a 90 angle results in an almost round drip stain whereas
a fall at an angle less than 90 leads to a more elliptic mark.
The more crooked the angle of impact of the falling blood
drop, the larger the degree of elongation of the resulting
bloodstain becomes as the width of the bloodstain
decreases and its length shortens. Exclamation marks or
thin, comma like structures can be seen at very low angles
(Fig. 4).

Fig. 3 Fall from 50 cm under various angels of impact

The same effect occurs when there is a relative movement between the origin of a blood drop and the horizontal
surface it lands on.
The swinging motion of a bloody hand, weapon or any
other object will produce bloodstain patterns on nearby
surfaces depending on the arc of the swing. This leads to
specific edge characteristics, such as spines. In order to
determine the direction of a blood stain one has to analyze
the long axis of a stain, since it defines two possible
directionalities of a given droplet.
When blood drops from a source with a fixed position it
will hit a fairly defined area. Droplets falling into an
already existing bloodstain (blood dripping into blood)
will create specific patterns, such as satellite spatter, from
which an indication of the height of the fall can be determined. At a low height an irregular but define outline with
a puddle like appearance can be expected. In the near
distance no or very few satellite patterns are likely to be
seen. With rising height the intensity and amount of these
satellite stains will increase, whilst their individual size
decreases. Furthermore, the radius of these small stains will
also enhance. An accurate height definition is not possible
by mathematically analyzing these stains, because of

Forensic Sci Med Pathol

individual surface variations on site, which also have to be

taken into account. Therefore it is sometimes essential to
do a reconstructional analysis at the scene with the corresponding material at hand. But in general a rough estimation on the area of origin can be done, for example to
differentiate between whether the person in question was
sitting or standing when injured.
Flow pattern describes a change in the shape and
direction of a bloodstain due to gravity and the angle of the
surface on which it is formed. Flow patterns and pools can
give important information about a victims movements
during the assault as well as post-mortem movement or
alteration of the body at the scene of death. These patterns
can for instance be seen on the body or clothing of the
victim as well as on the surface upon which the victim is
lying. As with most blood stains the kind of surface and its
angle are important in order to interpret these static
findings.
A blood pool is an accumulation of blood which can be
found at the lowest point of flow patterns. This pattern is
also an important static part of blood stain analysis and is
often the basis of transfer stain.
A so called transfer/contact pattern is formed when one
bloody surface comes into contact with another and blood
is transferred as a result of compression or lateral movement. Because of its strong adhesive force a blood transfer
like this happens easily, especially when the blood has not
yet dried. Contact patterns can give a good impression
about the shape and size of the objects in question (i.e. hard
object, finger prints, hair, body parts or shoe soleFig. 5).
Depending on the structure of a (shoe) sole, the ground
and the intensity of the steps (slow, careful steps vs. fast,
intensive running), these contact patterns can still be seen
after considerable distances (3060 m) from the crime
scene.
Fig. 5 a Contact pattern
between a bloody screwdriver
and fabric. b Contact pattern of
a bloody sole on paper

Additionally primary and secondary wipe patterns can

be differentiated. A primary wipe pattern is created when a
bloody object is moved tangentially on a surface leaving a
trace (so called swipe pattern). Secondary wipe patterns
occur when an uncontaminated, clean surface or object is
tangentially drawn over a pre-existing bloodstain (so called
wipe pattern). Wipe patterns can be helpful to determine a
chronological order of various incidents.

Projected patterns
Projected patterns are blood spatter, which are caused by a
force other than impact.
Arterial pattern is caused by a wound revealing an
arterial blood vessel. Blood which is not only affected by
gravity alone, but also accelerated by arterial pressure
leaves distinguishable patterns on surfaces which reflect
the course of the blood curve between the systolic and
diastolic phase. The arterial pressure first propels blood
upwards and then, with a decrease in pressure during the
diastolic phase within the cardiac rhythm, allows the blood
to drop downwards, leaving a zigzag-like formation.
Arterial gushes are normally of more volume compared to
other injuries, but also fine, small, so called spurts can
occur, especially when only a part of an artery is injured.
Because of the permanent flow of an arterial injury,
movements and their directions can be reconstructed quite
well.
Cast off patterns appear when blood is projected or
thrown onto a surface from a blood-bearing source or
object in motion (Fig. 6) such as blunt or sharp melee
weapons (a hammer or knife). In these cases an almost
linear cast off pattern is produced by quickly reaching
backwards, generating a centrifugal force which allows

Forensic Sci Med Pathol

Fig. 7 Expirated blood

Fig. 6 Cast off patterns from an iron bar, hammer and knife

adhesive blood drops to leave the object in motion. The

more forceful the swing is the smaller are the resulting
drops. Stains representing a low angle have the longest
distance to their source, while regular round patterns can be
seen as a direct hint to the positioning of the offender,
right-angled towards the pattern. Cast off patterns are
commonly smaller (\67 mm) than passive drop patterns.
Exhaled or expirated patterns occur when blood is
forcefully expelled from the mouth, nose or an open wound
as a result of air pressure. Often these patterns show bubble
rings as an effect of an exhaled blood-air mixture (Fig. 7).
The reasons for expirated blood can be manifold, for
example skull injuries, bleedings in the neck-region or lung
injuries. Even without an air-blood mixing, finer patterns
are possible, for instance if neck-vessels or the trachea is
damaged and the resulting blood drops are accelerated
against a surface. These microscopic patterns are created
by a nebulizer like effect (Fig. 8), whereas larger, more
irregular patterns are often caused by coughing or sudden
exhaling. Due to similar appearances these patterns can
easily be confused with medium or high velocity impacts.
Furthermore inhomogeneous surfaces like rough plaster or
wallpaper can simulate comparable effects.
Splash patterns are produced when a large amount of
blood comes in contact with an even surface at minor or
low velocity. These patterns usually have a large central
area with peripheral elongated bloodstains. They normally

Fig. 8 Accelerated blood

imply a cohesive impression with a slight separation in

smaller, spike-like patterns.
Spatter stains are the result of blood which has been
spread as a result of force applied to a source of fluid blood.
Forward spatter, caused by a movement in the direction of
the force and back spatter, created by an opposite movement, can be differentiated. In this context, an impact is
any kind of blunt trauma strong enough to disturb a
homogeneous pattern by overcoming its surface tension

Forensic Sci Med Pathol

and forming smaller, finer stains. The higher the energy

level, the smaller are the resulting spatter stains. It is
therefore possible to differentiate between low, medium
and high velocity impact spatter.
Low velocity impact spatter
At low velocities the resulting force or energy meets the
average gravitational force at velocities up to 1.5 m/s. The
outcomes are relatively large ([ [ 4 mm), often irregular
spatter stains within a rather small area. Centrally pointed
or elongated stains can be detected (so called spines).
Medium velocity impact spatter
Medium velocity impact spatter are bloodstains between 1
and 4 mm in diameter, which are produced on a surface
due to a medium velocity force between approximately
1.57.5 m/s to a blood source. Beating with a solid object
is a typical example for a medium velocity impact. In these
cases irregular shaped patterns with sometimes larger
volumes and overlapping patterns, such as splashpatterns
(a low velocity impact upon a quantity of blood) can be
seen.
High velocity impact spatter
When the source of blood is subjected to a force with a
velocity of approximately 35 m/s or more the major part of
the resulting spatters are less than 1 mm in diameter, even
though larger stains can be observed within the pattern.
Usually high velocity impact spatters are associated with
gunshot injuries, where high quantities of energy affect a
fairly small area.

the direct result of surface tension and the adhesive forces

of liquids when in contact with hard objects and may cause
blood to be drawn towards an object, opposing gravity.
This attraction may result in blood stain patterns for which
there is no matching defect. Linear stains or linear accentuations within an area of bloodstain pattern are typical
examples for this phenomenon.
Void pattern
If an object is placed between the blood source and projection area, it is likely to receive some of the stains, which
consequently leads to an absence of stains in an otherwise
continuous bloodstain pattern. (Figs. 9, 10). A void pattern
always indicates that another object was present and/or
involved in the incident. If the object in question has been
removed, it might still be possible to reconstruct its shape
by examining the outskirt of the void.
Skeletonized stain/perimeter stain
If a blood stain is disturbed before having dried completely
its original shape and size can still be seen (Fig. 11). This
resulting effect is referred to as skeletonization. Blood will
usually begin to dry from the outer parts inwards toward
the center of the stain. The time a blood drop takes to dry
depends mainly on the surrounding temperature, air

Secondary changes
Insect stain
Fly artifacts are small, spatter-like stains of blood as a
result of fly activity, which easily can be mistaken as drip
pattern, expired blood or high velocity spatter. Benecke
and Barksdale examined irregular bloodstains at crime
scenes and validated their logical relationship to the scene.
In their research they established criteria such as geometric
patterns, lack of spiny edges, logical convergence, etc., for
distinguishing fly artifacts from human bloodstains [9].
Capillary action
Capillary suction of objects or edges leads to an additional,
mostly mechanical distribution of blood patterns. This is

Fig. 9 Void pattern

Forensic Sci Med Pathol

Diffusion
When blood comes into contact with clothing and fabric it
spreads via diffusion, often leaving an irregularly shaped
pattern which is difficult to interpret, especially if the
clothing has not been secured properly.
Projected blood stain pattern

Fig. 10 Void pattern

Projected blood stain patterns are produced when blood is

spread on a target under pressure as opposed to an impact.
Arterial spurt or gush is a typical example for projected
blood stain.
Machinery with fast moving body parts, such as a chain
saw, can accelerate blood quite fast, which then causes a
typical pattern on the projected surface (Fig. 12).
If a certain amount of blood stain can be associated with
one incident, it is important to determine the point or area
of convergence, i.e. the location from which the bloodstain
originated. This can be done by calculating angles of
impact of well-defined stains back to the long axes of the
bloodstains through the point or area of convergence. Since
both the villain and the victim are in motion during the
incident, the area of origin is a rough estimation, rather
than an exact mathematical determination of one point.
However, it is possible to differentiate whether the victim
was in a standing, upright position, kneeling or lying on the
floor at the time the injury occurred. Additionally, different
areas of convergence can point out different positions of
the victim during the incident. Different movements can be

Fig. 11 Skeletonised blood

humidity, wind speed, insolation, as well as size and

thickness of the stain. Under usual Central European climate circumstances, in a closed room, smaller bloodstains
will dry within 1020 min. The resulting skeleton cannot
be used as a basis for exact calculations considering its
origin, but it can be a useful tool to estimate a time frame
between its occurrence and blurring or to evaluate
sequencing of incidents. In this context it sometimes is
necessary to validate ones theory with experiments under
similar circumstances on site.

Fig. 12 a, b Projected blood by a chain saw

Forensic Sci Med Pathol

reconstructed and the amount of impacts on the source of

blood can be estimated.
There are some computer programs which calculate the
area of origin within a 3-dimensional set up, but in practice,
the stringing or tangent method has been shown to be a
reliable technique to evaluate the area of convergence.
Strings are positioned through the axis of each of a number
of spatters and then extended backwards in the direction of
where the drop originated. The crossing point of these lines
indicates the area of impact.

Luminol
Since 1930 luminol has been used as an additional searching technique to detect hidden blood stains [10]. Luminol
(3-Aminophthalacidhydrazide) exhibits chemiluminescene
in the presence of blood, when mixed with an appropriate
oxidizing agent (H2O2 and NaOH). The iron found in
hemoglobin catalyzes the chemical reaction, leaving a
striking blue glow, which lasts for about 30 s (Fig. 13).
The best known instructions on how to compose luminol-solutions are by Carter [11] and Lytle and Hedgecock
[12]. The recipe by Weber is more sensitive and is produced with three solutions:

8 g NaOH in 500 ml Aqua dest.,

10 ml of a 30% H2O2-solution in 490 ml Aqua dest.,
0.354 g Luminol in 62.5 ml 0.4 N NAOH-solution,
Aqua dest. ad 500 ml.

If the H2O2 is not older than 8 weeks, these standard

luminol solutions are stable for several months and highly
sensitive for 812 weeks (11).
Luminol is used to identify minor, unnoticed or hidden
bloodstains diluted to a level of up to 1:106 (1 ll blood in 1 l
of solution). The mixed substances are directly sprayed onto
suspicious areas, usually in a completely dark environment.
If the reaction is positive, the chemiluminescenic reaction
can be photographed while the luminescent areas are marked
in order to investigate them once the light has faded.
Luminol has a high sensitivity for blood, especially for
older, completely dried blood (Pex, IABPA News 2005).
Unfortunately, the luminol reaction is not triggered by blood
alone, and a rather wide range of environmental and pharmaceutical substances such as detergents, some metals and
vegetables can influence the process [13]. Since there are a
number of substances interfering with the luminol reaction
and possibly leading to wrong conclusions, it is essential that
the forensic practitioner is aware of these disadvantages [14].
Experienced analysts are able to recognize visual differences, depending on each chemical reaction with luminol.
Apart from luminol, there are other substances that are
able to detect hidden blood stains, for example Blue Star.

Fig. 13 a, b Luminol related blood reaction

This solution, commercially produced in France, shows a

stronger visual reaction with blood at high blood concentrations, but has a minor sensitivity at lower blood concentrations. Both substances, luminol and Blue Star usually
allow a reliable DNA-analysis after the application [10, 15].
Sideeffects of luminol have not yet been fully examined. There are however reports on mucocutaneous irritations of the eye, skin and gastrointestinal tract with
diarrhea and vomiting. Due to this, it is advisable to ensure
fresh air circulation after having used luminol. There is no
evidence concerning chronic effects [14, 16].

Presumptive testing for blood

Suspicious stains can be tested for blood with presumptive
blood tests, such as the Combur Test, manufactured by

Forensic Sci Med Pathol

companies like Boehringer or Roche. These are plastic

reagent strips, which are used in clinical laboratories to
detect occult blood in urine. The test is based on the peroxidise-like activity of hemoglobin catalyzing the reaction
of disopropylbenzene dihydroperoxide and 3, 30 , 5, 50 ,
tetramethylbenzidine. If the testing is positive, the area in
question can be secured for further DNA-examination.
Presumptive tests are an additional tool to differentiate
between positive and false-positive luminol reactions.

Examination of the crime scene

Blood stain pattern analysis of a potential crime scene
should consist of the whole area in question, including its
peculiarities considering mobile or fixed objects as well as
its three dimensional conception. An initial review of the
crime scene should be the first approach of an analyst in
order to get an overview of the layout of the scene,
bloodstain location, physical evidence, the victims location, etc.
A written and photographic documentation of the scene
and bloodstaincomplexes is necessary, using specific terminology. In order to maintain an objective view the first
step of examination should only be the documentation
process of possible relevant stains or suspicious areas.
The interpretation of the crime scene has to be strictly
separated from the primary examination. Here a subjective,
evidence- and experience- based point of view is unavoidable and often necessary, especially since sometimes more
than one explanation might be possible. A specific interpretation of a crime at a very early stage should therefore be
avoided. In order to be able to give a full and satisfactory
interpretation of a crime scene it is fundamental to gather as
much information (DNA-testing, autopsy-report, laboratory-reports, etc.) as possible, before making a final
statement.
Crime scene reconstruction
When reconstructing a crime scene, certain aspects have to
be taken into account. If blood stains are not fresh, i.e.
completely dried, a temporal allocation of the incidents is
difficult. With the course of time, the color of the dried
blood will darken from a dark red to dark red-blackish to a
brownish coloring with possible fragmentation within larger adhesions. Smaller or very thin stains often dont show
fragmentations. This can be of importance at crime scenes
where there have been a number of physical arguments
with possible bleeding injuries some time before the deadly
incident. Blood stains do not necessarily have to be from
the victim. Blood stains which dont fit the pattern and
cannot be associated with the injuries of the victim could

be seen as possible stains from the offender. These spots

should be examined further (e.g. via. molecular biological
methods). Sharp force in particular is often related to
injuries on both sides, the victim and its perpetrator, so that
a detailed separation of blood stains can be very helpful
reconstruction work.
And even after accurate cleaning efforts it is often still
possible to detect small fractions and even larger areas of
blood stains at a crime scene [17, 18]. After a cleaning
process stains can be seen with the help of detection systems, such as the luminol chemiluminescence reaction
[19]. For this, sometimes an additional crime scene
investigation with adequate photo documentation can be
necessary. But before an excessive and often costly analysis like this is initiated, all background information should
be present, and especially doubtful stains should have been
identified beforehand (falsification and alteration of complex blood stain patterns with animal blood are quite
common, particularly in messy householdsa female
dogs heat period).
Blood and bloody liquids can enter the smallest gaps or
crannies due to the already mentioned capillary suction,
especially after a cleaning process (diluting effect). If
necessary it might be helpful to remove carpets or floorings, primarily wooden flooring such as parquet in order to
be able to estimate the extension of the original blood
stains. Sensitive pretesting of hard accessible areas such as
drawers, under window boards or in cupboard gaps can
give important hints where to investigate further (e.g. with
the help of luminol).
Documentation and evaluation
The correct inspection, identification, documentation, collection and conservation of physical evidence is fundamental to the efficient reconstruction of a crime scene.
It is important for the medicolegal death investigator to
be knowledgeable about the death scene. Therefore a primary, systematic inspection of the whole crime scene is
essential in order to gain an objective overview. All types
of physical evidence should be inspected. This sometimes
allows an early judgment considering the victims or suspects variant of the crime. However, written statements
should be composed carefully, since these statements can
change easily during trial. Early statements or too speculative conclusions might compromise later crime
reconstructions.
Accurate and objective documentation is truly an
important part of bloodstain pattern analysis. Detailed
photo documentation is one of the most important parts.
Since crime scene photography has some unique requirements the following principles should be taken into account
[20]:

Forensic Sci Med Pathol

Photos should always include a standardized scale

and a fixed object in reference to the blood stains
documented,
good lightning,
overview shots as well as detailed photographs,
detailed photographs should easily be recognized
within overview shots,
an upright position of the camera in reference to the
surface being photographed,
the use of a 50 mm objective lens, if possible.

If a crime scene is not accessible, a blood stain pattern

analysis might be possible by photographs alone, but with
the correlative limitations (photographic angle, exact measurements, etc.).
Secondary alterations by emergency physicians or first
aid personnel have to be noted and taken into account.
A sketch or diagram of the scene with correct measurements, accurate distances and relative proportions is a
valuable complement to the photographs taken at the scene.
As an additional tool it helps explaining investigative
data to make the whole situation easier for everyone to
understand.
The use of computer based blood stain pattern analysis
such as Back Track is currently mainly experimental [21].
To our knowledge the available computer programs are
rarely used in routine work. Since this part of blood stain
analysis is fairly new, recent studies and developments are
promising [22] and one can expect these programs to be of
great assistance in the future.

However, the interpretation of blood stain pattern is

apart from forensic and medical knowledgemainly based
on experience and requires constant theoretical and practical education and training (Appendix).

Key points
1.

2.

3.

4.

Appendix: CME Questionnaire

1.

Preserving evidence
Physical evidence on hard, immovable objects is usually
transferred and secured by standard molecular biological
methods. The method which is used to collect evidence
depends on the type of evidence and the location from
where it is being taken. The best form of preservation is
first to photograph the area in question and then take the
evidence with the required method to prevent contamination with other substances.
Depending on the importance of each blood stain, it is
sometimes necessary to preserve whole objects in order to
analyze them later under controlled laboratory conditions.
For logical reasons the analysis of blood stains, its origin
and importance should be carried out by forensic pathologists. Their medical background gives them a greater
knowledge on various possible wound mechanisms that
may or may not lead to the results at hand. Ideally the
forensic pathologist who performed the autopsy also takes
part in the crime scene investigation and the analysis of the
blood stain pattern.

BPA is a useful contribution to the crime scene work

and the collection, categorization and interpretation of
the shape and distribution of bloodstains connected
with a crime.
The shape of a bloodstain depends on the four phases
of impact, which are, among others, influenced by the
dropping height, angle of impact, surface texture and
velocity of the droplet.
The following basic groups of patterns can be divided:
dripped and splashed blood, projected blood, impact
patterns, cast-off stains, expirated and transferred
bloodstains.
By examining blood stain patterns and evaluating their
origin, BPA offers a functional, medically and scientifically based reconstruction of possible wound mechanisms that lead to the results at hand.

2.

What shape does a free falling droplet have?

h Ellipsoid.
h Sphere.
h Tear-drop.
h Long.
h Triangular.
Which statement about the behavior of blood is
correct?

h Small droplets fly over a longer distance than bigger

ones.
h Blood droplets always have the same volume, independently from the shape and surface of the subject
they originate from.
h Falling or accelerated blood oscillates a little bit.
h The viscosity of blood is slightly higher than that of
glycerine with the same temperature.
h Free-falling blood droplets separate into smaller
droplets when falling from a height of 3 m or more.
3.

When a flying drop of blood hits a surface four phases

of impact can be differentiated. Which of the following
is wrong?
h Diffusion.
h Contact.

Forensic Sci Med Pathol

h Shifting.
h Dispersion.
h Retraction.
4.

Which of the following blood stain patterns are not

projected patterns?
h
h
h
h
h

5.

What can be determined from a bloodstain pattern?

h
h
h
h
h

6.

The surface structure of the point of origin.

Angle of impact.
Age of the blood.
Human or animal blood.
Blood of a living or a dead person.

What typical form can be seen in a cast-off pattern?

h
h
h
h
h

7.

Arterial pattern.
Cast-off pattern.
Exhaled or expirated patterns.
Inhaled pattern.
Passive drop.

Y-shape.
Double punctuation.
Question mark.
Exclamation mark.
Slash.

Which statements considering primary and secondary

wipe patterns are true?
h A primary wipe pattern is created when a bloody
object is moved tangentially on a surface leaving a
trace (so called swipe pattern).
h Secondary wipe patterns occur when an uncontaminated, clean surface or object is tangentially drawn
over a pre-existing bloodstain (so called wipe
pattern).
h Wipe patterns can be helpful to determine a chronological order of various incidents.
h Secondary wipe patterns are almost always the result
of arterial bleeding.
h Primary wipe pattern can only be created by arterial
bleeding.

8.

Which sentence is incorrect?

h If the object in question has been removed, it might
still be possible to reconstruct its shape by examining
the outskirts of the void.
h Blood will usually begin to dry from the outer parts
inwards, toward the center of the stain.
h Projected blood stain patterns are produced when
blood is spread on a target under pressure as opposed
to an impact.
h Arterial patterns dry faster than venous ones.

h A blood clot describes the final product of blood

coagulation.
9.

Which of the following statements are incorrect?

h Luminol is used to identify minor, unnoticed or hidden bloodstains.
h Luminol gives a positive reaction to some vegetables
and metals.
h After having used Luminol a DNA-analysis is not
possible.
h In order to get a perfect result when using Luminol it
is important to light up the room.
h The mixed Luminol solution is directly sprayed onto
suspicious areas.

10.

Which statement considering documentation is

wrong?

h Photos should always include a standardized scale

and a fixed object in reference to the blood stains
documented.
h In order to maintain an objective perspective, an
upright position of the camera in reference to the
surface being photographed is essential.
h If a crime scene is not accessible, a blood stain pattern analysis might be possible by photographs alone.
h Overview shots are not important, since the details of
a pattern matter, when calculating the angle of
impact.
h If necessary, physical evidence on hard, immovable
objects can be transferred from the crime scene and
looked at separately.

CME Questionnaire answers

1. Sphere
2. Falling or accelerated blood oscillates a little bit
3. Diffusion
4. Inhaled pattern
AND
Passive drop
5. Angle of impact
AND
Blood of a living or a dead person
6. Exclamation mark
7. A primary wipe pattern is created when a bloody
object is moved tangentially on a surface leaving a
trace (so called swipe pattern).
AND
Secondary wipe patterns occur when an uncontaminated, clean surface or object is tangentially drawn
over a pre-existing bloodstain (so called wipe pattern).

Forensic Sci Med Pathol

AND
Wipe patterns can be helpful to determine a chronological order of various incidents
8. Arterial patterns dry faster than venous ones
9. After having used Luminol a DNA-analysis is not
possible
AND
In order to get a perfect result when using Luminol it
is important to light up the room
10. Overview shots are not important, since the details of
a pattern matter, when calculating the angle of
impact.

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