I don’t know. Columbo looked pretty perplexed as he was leaving the office.

Dr Mayfield should have retrieved the suture from the coat that Columbo was wearing immediately, and put it in his pocket and then there would be no evidence left. then he could have discarded it at some later time. but not in his office. as soon as the door shut and Columbo was gone, he should have done just that. and then he would have been home free

He would have had to do it quick because Columbo came back right away. And if he did and if the coat was moved even slightly Columbo would have noticed and could have searched the doctor again