When I first started watching Columbo as a kid, I hated the fact that it showed the murder being committed at the beginning, showing who did it before the mystery started! It completely took away from the concept of following the detective through the case, trying to figure out who the murderer was. It wasn't until recently, when I started watching it again, that I realized that I wasn't supposed to see the story from Lt. Columbo's perspective, but from the killer's perspective. The killer is the star of his/her own episode. We are shown why they are driven to kill their victim, and sometimes we even sympathize with the killer. We feel the same anxiety that they do when Columbo gets closer and closer to pinning the crime on them. And, most importantly, it makes it impossible for the writer to pull an impossible reveal out of their ass at the end. - Japper8
To add to this; this means that the star of the show, the hero the audience is expected to root for, is not the protagonist but the antagonist. ~ Doctor Nemesis
Columbo has a glass eye; as he already Doesn't Like Guns, that would make effective shooting in an actual fight much harder.
Why does Columbo always run his theories by the murderer? Making them sweat is fun, but it also tips them off and makes them much more likely to try and cover their tracks. Why take the risk? Then I realized—All the evidence he brings them? It's circumstantial. He is making sure that he has a rock-solid case that no one can disprove, and he tests it by bringing it to the murderer. Who would be more interested in disproving his case than the person who did it?