It was Agenda for murder for clarification purposes.
I always thought that due to the mention of columbo sloving the murder on board in troubled waters that A matter of honour was the very next episode (columbo gets off boat and word has spread) and therefore was suprised to find a while back that they are from different seasons.
And the first time he ever refers to a previous case is in Double Exposure...he comes in and says he was working late on that Hayward case....referring to Candidate for Crime.