Do you think Columbo realized before he walked out of the office that the suture was put in his pocket? Perhaps he realized right when the Doctor bumped into him or some other time on the way to the office or before leaving, and he left and came back to string along the killer or to shock him.
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