I'm bringing this up just for the sake of it, as one more thing to bring up.
Everyone knows he never threatens anyone with a gun, but does he ever risk the killer's life (or anyone else's), without meaning to? There are a few cases where that COULD be true.

A MATTER OF HONOR - When Luis freezes up a second time, MAYBE that bull could do him some harm before they get him under control.
SHORT FUSE - Rodger could do himself some kind of harm thinking that the exploding cigars are in the tram car.
LADY IN WAITING - Columbo's sneaking into the house causes Beth to point that gun at him, and there are other police right outside. Of course, in COLUMBO, you never see OTHER cops shoot people any more than you see HIM do that, but it could still be pretty risky.

in Murder Under Glass he switched up the wine glasses. Just as the killer was about to take a sip Columbo said no, I wouldn't do that sir. Something to that effect.

The second part of your post is very interesting. It's true you never see anybody get shot in that series by the police. As a matter of fact, there's one episode where Columbo looks completely lost when he's holding a pistol. I forget exactly which one that was. There was also another episode where he had to have his Sergeant qualify for him, I think it was in forgotten lady, because he could not hit the target

In one of the newer episode when Columbo was undercover, didn't he pull a gun on Burt Young in the hotel room?