Movie originally had different ending which instead in sewers took place in some warehouse and was lot less action packed. Following the successful test screening producers gave the filmmakers some money and short amount of time to film the new, more exciting ending and to add sequel bait last shot because they already planned to do sequels. Not much is know about original ending or if it still exists, but there are many stills showing parts of it.
During filming, numerous press materials listed the title as "Transit" - because of the killer's ability to jump between bodies as a way of moving around the city. Orion, the film's US distributor, decided in post-production to re-title the film "The First Power" so potential audience members would be more aware of its supernatural/horror elements.
Stewart Copeland, Drummer and Founding Member of The POLICE, Composed the Music for The First Power.
In the scene where the killer appears to jump off the building from about five stories high, lands on his feet, then runs away, was actually performed by the stunt double without any special effects. Bar the cable noticeably attached to his back, and it was ten stories high.
The poster for this movie appears in the Seinfeld episode The Dog.