2 questions about wife catching a murdering husband

I have a tricky question, I won't go into the details of the whole plot or it would take me ages, Anyway. Woman has lover, husband finds out and decides to kill him. He happens to kill the wrong man, a friend of the woman's lover's who has similar build and was in the lover's house. When he realises his mistake, he decides to get the wife's lover framed for the murder (I have this all worked out). The lover goes to jail and the killer and his wife decide to try and move on. Except----- the wife finds out that her husband is the true killer - so my question is, HOW does she find out? It would have to be serious enough for her to be able to prove it to the police. Computer files wouldn't work, he's not that stupid (and he's a dentist if that can be of any help)

Question number 2. I want the husband dead by the end of the novel. In the beginning I was thinking the wife could kill him, but that would make her look too evil to the reader and I don't want that (even self defence would be a bit of a cliché). I want his death to be an almost accident where maybe, just maybe the wife could have saved him, but decides not to at the last second.

Thanks guys

Thanks! The kiler frames the lover by placing his blood all over the crime scene. The lover is an ex drug addict and he (being a doctor) manages to inject him with drugs and of course then it's easy to get his blood and finger prints all over the crime scene. How can the wife catch him? I was thinking blood-stained clothes in the washing machine which she becomes suspicious of and puts aside.... but is that too obvious?

Also, I would like thte husband to die in an accident which she might have saved him from..... so that she doesn't look totally cruel, but not 100% innocent either

thanks, but the how could I frame the real lover?