Jared Leto's character was guilty
of 2 counts of Obstruction of Justice. (Lying to the police during the course of an investigation)
Apparently, years ago, he walked into the police station, confessed to murder and then after wasting some detectives entire day, he says "J/K", "You've been punked".
No way they let him loose without charging him.
After wasting the police's time again and threatening his family, Detective Baxter should have no trouble sleeping at night, even if the murders continue.