This is a very good point. And even before that, I can't understand how a team of highly skilled surgeons who had been instructed to watch Dr. Mayfield's every move would fail to see what happened to the dissolving suture that was already in Dr. Heidemann's heart.

He plants evidence in s2e4 - the ep in England. Had the individuals been innocent, they would have been convicted unfortunately because of Columbo's guesses.