Recently, I have been watching the entire "Columbo" series via DVD's. Many of the actors in the early shows (in the 1970s) are dead. Oh well, we all die. Then, what happens? In any event...
Many of the alleged murderers in the show had incriminated themselves, but had not been warned of their right to be silent. Specifically, Columbo never told suspects that "You have a right to be silent..." etc.
Thus, the alleged perpetrators' statements, triggered by Columbo's conversations and accusations, could possibly be eliminated from trial. And so, some of the guilty persons Columbo arrested could go free. Depends on the evidence, of course.
There should be a TV program about what happens after Columbo arrested the alleged murderers, and the trial begins. That could be a show. We'd need a new Columbo, as Peter Falk died over ten years ago. https://en.wikipedia.org/wiki/Peter_Falk