#17 - It is lawful for police to lie in certain circumstances. The landmark decision regulating false statements made to a suspect is the U.S. Supreme Court case of Frazier v. Cupp, 394 U.S. 731, 1969. The case involved the interrogation of a homicide suspect who was falsely told that an accomplice had already implicated the suspect in the killing.
This was a terrible decision because it opened the door to what goes on today. Once you are legally allowed to be untrue, human nature takes over and then we find police expanding this practice to cover other areas such as writing reports, court testimony, etc.
Combine this with the 'law and order' mindset of prosecutors, judges and the rest of the criminal justice system, it becomes an accepted practice to help get indictments and convictions, which is their job/goal.