Frequently, in various episodes, the detectives say that a gun is registered to someone (or that someone has no registered guns, or the like). There is no gun registration in Pennsylvania; it's prohibited by state law.
In multiple instances, the squad's detectives employ threats or coercive tactics that would either damage the case or result in possible acquittals. On several occasions the captain (the squad's leader) is involved in these interrogations which would result in his dismissal from his job.
Multiple cases are shown to have occurred involving juvenile killers. These cases would likely be adjudicated quickly and the defendant being briefly jailed or even released as such cases are difficult to try and mature adults can not be held in juvenile facilities.
Throughout the series the detectives interview people years (sometimes decades) after the crime takes place, and yet they all seem to remember it like it was yesterday and are able to give accurate detailed descriptions to the police.