And #4 is Luis Montoya in Matter of Honor
and I think #1 is Prescription Murder - I think it was Ray Fleming to Burt Gordon (or was it Burt Gordon to Ray Fleming??)
Yes, they are both post-70's episodes. #1 is Congressman Mackey to Oscar Finch in "Agenda for murder". #2 is the male killer to the female (played by Shera Danese) in "A trace of murder".
#4 is the guy from the Winston Insurance Company, in "Identity Crisis". #6 is a woman at the carnival that Columbo showed the picture of dead Geronimo to.