It's ambiguous, so it wouldn't count as a goof...but I have always gotten a little agitated at the moment in "Prescription Murder" in which Carol Fleming turns away from Ray toward the windows just before her death. He has been hiding the fact that he is wearing gloves, yet at that moment her eyes go down and it looks to me like she looks straight at his hands.
Every time I watch this episode, I expect her to say something about it...like, "Why are you wearing blue gloves???!!!"
I am bothered by the fact that Dr Flemming has such a big mouth and said such stupid, arrogant things at the end that he ended up hanging himself. It is a good story, but that struck me as just too much, it seems the writers didn't know how to end it. Later episodes were more clever.
The first ending for this story (the 1960 TV movie, "Enough Rope") indicated that Columbo -- as a result of other clues -- was going to drag the bottom of the lake where Fleming had dropped the supposedly stolen goods, until he found everything.
This would be pretty strong proof, assuming the stuff was uniquely identifiable. (Why would the supposed burglar/murderer have flown to the same vacation spot where Fleming was, then dumped the goods that he had committed murder to steal? Unless it was a very elaborate plot to frame him --- good luck with that defense, doc.)
See the Scrapbook article, "Enough Rope -- the Very First Columbo", which also summarizes yet another ending, used in the stage version of "Prescription: Murder".
It seems that Levinson and Link made a conscious decision to make Columbo's solution be based his mastery of psychology, his ability to read the suspect's character flaws, and his penchant for staging scenes and setting traps that the killer will jump into. (Instead of on conventional physical evidence, as in the original version.)