FAQ

It's a strange wording indeed, that would imply that they are murderers. It's probably a play on words. Later, after both their real lives spouses died under mysterious circumstances, and they were both real life suspets for a time, the words were changed to remove "it was murder!"

The above is an interesting theory from another reader; however, the change may actually be far less sinister. In Hart to Hart episode "Two Harts Are Better Than One" from Season 5, there's a look back to when the Harts met and there was, indeed, a murder in that episode. If the backstory was known from the beginning (although not known to viewers), this would explain that original intro.