This one is really reaching, but Lovely But Lethal and A Stitch In Crime each have someone who isn't an accomplice but who has a real thing for the killer. In the one it's Murcheson and in the other it's Marsha.
1. What do Lovely but Lethal and a Stitch in Crime have in common?
They also partially share the same set! Take a close look. The lab in "Lovely but Lethal", with the unique observation windows overhead, is the same room as the Operating Room in "A Stitch in Crime", where the observation deck is used.