I'm gonna guess at the bye bye sky high..just because Bertie (that is the victim's name right?) kind of stutters and stammers and could probably have said I five times altogther. And also I don't think that episode has been used yet. And Cassa, now you know what its like to come when most of the answers have been got...but now you have to tell everyone that you knew them anyway..
Trying to remember as best I can in review of the 45 original episodes, the two I come up with as strong possibilities of the victim using five "I"'s in their last three sentences are "Murder By the Book" and "Requiem For a Falling Star." Hopefully at least one of these two is correct.