You could add Paul Galesko throwing
the photo of Frances tied up that he didn't like into the fireplace. I think
the point is that these people, as cold-blooded killers as these people might like to think of themselves, when they actually do it, they are not thinking 100% straight
and make stupid mistakes. I think that is quite realistic.
Alex Benedict did many other stupid things, like picking up the flower and putting it on so demonstratively in front of Columbo (he could have just as unobtrusively put it in his pocket). Also, he as a "disinterested bystander" was really dumb for insisting "it had to be a suicide". He should have said "Lieutenant, you think it was murder-find the dastardly person who did it!".

Alex not noticing that the flower fell off is much more acceptable that Cahill's actual lighting of a match and cigar at the scene of a murder he just committed. Cahill was supposed to be of genius. Genius should have surpassed his angst at the site of his dastardly deed.

I realize that Peter Falk loves the cigar-match clue. My big problem with it is that it's a very "forced" clue. Cahill lights that match and leaves it at the scene merely because the writer of the script needed him to light it and leave it there for Columbo to find. Otherwise, it doesn't fit with the intelligence of the murderer involved. Alex Benedict not realizing that the flower has fallen off his lapel at the site of his dastardly deed is much more acceptable to the character and the situation.

I was just thinking a bit further about Cahill lighting up that cigar. I think that if there had been enough time to allow it, a full scene of Cahill sitting back and enjoying the cigar and a glass of wine - perhaps even reading some pages of a fine classic book - all while the dead body of his ex-friend lays at his feet... I would have to say that such a scene would played out better. It would have set up the Cahill character as a true fiend, capable of smoking a cigar over his dead friend's body. If this had occurred, then the cigar-match clue would have been more acceptable.

Another murderer who was suspiciously non-receptive to Columbo's theories was Emmett Clayton. Clayton should have been aware that after Dudek was murdered by the tampered medications that that would close the book on any remaining "accident" theories, so he should have tried "playing along" with Columbo more.

Clayton could have made up a story about Dudek expressing concern to him the evening before in the restaurant about a feud he was having with one of his countrymen. Or maybe Clayton could have said something about some anti-Communist phone call Dudek just received, but Dudek was afraid if he told his coach, he would cancel the match.

Clayton should have known that sooner or later Columbo would be looking for a murderer. Clayton should have agreed with Columbo and tried to point suspicion elsewhere.

Hi Steve
The lost flower could easily have been dropped, simply as a mistake and forgotten.But that was Benedicts downfall, wasn't it.
The Whiskey bottle wouldn't have meant much had Devlin not marked the bottle with his ring, also his downfall.But what about the missing weapon Robert Culp used, it just melted away.But Columbo guessed but never actually suggested a piece of ice was used.
That is surely the beauty of the writing.