Some Killers by trying to cast suspicion elsewhere or provide the perfect allibi (Like Milo Janus) often hang themselves in the process. For instance:

Wade Anders. If he never offered up that video tape as evidence that he was in his Production Studio, Columbo would have never solved the case. Because by going to the studio to pick up the tape, that's when Columbo noticed that his car had scratches on it. Which ultimately led to his arrest. And of course the tape was tampered with. So if Anders doesn't do that, he probably walks. Because everything else was circumstantial

Col. Rumford. The whole thing with the cider incident hung him out to dry. He was so clever to become an army colonel yet he was so stupid in knowing or not knowing that you could only see The Cider jar from one spot in the military yard.

Danzinger. The whole glove thing hangs him yet why does he hide them in the firehose in the 1st place?

just some observations I'm sure that you folks can brainstorm and think of some others

Speaking of Wade Anders, what was the point of putting one of his old stories under the dead man's hand? Not only did the typeface of the title tip Columbo off, so did the missing fingerprints on the back of the paper. Then there are the cigarettes. With as much as the victim smoked, he should have grabbed one of the other used ashtrays and dumped some into the one on the desk. It's almost like Anders was just asking to get caught.

Anders was about as dumb as they come. Esp. for a man who hosted a crime show.