Some of what everyone here has mentioned reminds me of two things, one Batman related, one not.
1. OFFICER DOWN revealed that the man who shot Commissioner Gordon joined the Gotham PD for the express purpose of getting close enough to Gordon to kill him. They even explained how the GCPD were hurting for applicants after No Man's Land.
2. In the first season of BONES, a killer on Death Row (at first saying his was innocent) dropped hints so Brennan and Boothe eventually discovered his other victims. The killer explained that he would have to go on trial for those murders, thus delaying his execution for years. He even said "Maybe by that time they won't have the death penalty anymore."