Can you explain the last 5-10 minutes to me?

The entire criminal underworld is ready to tear Peter Lorre's character apart because his crimes against children are the most despicable imaginable even among thieves, whores, etc., But his lawyer argues if he was crazy, as was suggested by his story of the only time he doesn't hear voices telling him to kill was WHEN he was killing, then it's not his fault, his appointed lawyer and the rest of the kangaroo court barter back and forth on where his accountability lies, but the rest of the court doesn't care, so they get ready to charge him and kill him, and that's when the police come in and bust them all, and he's carted off for a real trial, where it doesn't matter what the verdict is, if it's not guilty by insanity, guilty, guilty with a life sentence, guilty with a death sentence, it is irrelevant because no verdict is going to bring the dead children back to life, and the only thing that's going to prevent other people from committing more murders is the parents watching their children instead of just trusting they'll be fine.

The ending isn't ambiguous. The judge puts on a black cap just before pronouncing sentence; the black cap indicated a sentence of death was coming.