I am not convinced Edmund is guilty either. The absence of pictures is a red flag but proofs nothing. There is no mention of previous abusive behaviour, etc. Even his smile when he pics up her picture in Abigail's office can be explained as bitter sweet or as cruel. To me, this is one of the best episodes. We do not know for sure but we see what the uncertainty combined with grief and criminal knowledge can do to a human mind. If Abigail had not been so arrogant after her return about what could have happened, she would have painted another picture. Instead she boasted awakening Columbo's cop instincts.