"Whose fault is it?" -- an open-ended riddle

[ScioAgapeOmnis]

1) Killer - because he chose to kill her.
2) Mary - because she went back to the bridge with the killer on it, among many other stupid choices.
3) Lover - It is unlikely she'd just lie to him about this. However, maybe she would just to get his pity. And maybe he's just so emotionally blocked off right now that he really just doesn't care about anything she says. Or maybe she has a history of making stuff up like that anyway. Or maybe he believes her and is just a psychopath. But it doesn't matter - I'm not sure what she expects him to do anyway, go kill the killer? It seems that there's little he can actually do to help her - nothing that she can't do herself. She needs to go to the cops, or whatever is the equivalent in her world.
4) Ferryman - Maybe he thought Mary was making things up to get a free ride. He doesn't know Mary so the latter is a plausible suspicion. But either way going on a boat when the killer is on the bridge is dumb anyway, he can meet her on the other side and then what is she gonna do? No, if anything, he'd just endanger her by taking her on the boat.
5) Husband - No matter who or what he is, everything that happened to Mary was a result of her choices and hers alone.

 

[Buddy]

I like to over-analyze riddles sometime, because I've been fooled by so many riddles over the years.
It was a joy to follow this thread because to me, it seemed to be mostly an example of how we allow our thinking to be led by others through our assumptions.
The riddle, itself, is loaded with assumptions. Even the question at the end assumes itself to be valid.
The first part "Whose fault..." implies looking over the cast of characters and picking one, however the instructions are to pick everyone and assign a fault percent. If you do that, it seems to me that attention towards the killer is being purposely diluted to make it easier to get him/her acquitted.
Yes, I do see that there are a lot of issues and dynamics involved, including the fraud/deception against the husband by violating exclusitivity agreements (and that assumes they weren't swingers :O ), but I think the killer is the only one who is responsible for Mary's death, simply because "the killer" is the one who killed her.
We don't even know if Mary's indiscretions explain why the killer was there to do the dirty deed. :)

All in all, I think I identified more with RedFox:

Having read that a few times I find myself wondering what sort of person wrote this 'scenario'.....theres a lot of pathology in it. I choose not to answer it how it 'says' I should :P

 

[Telperion]

oh, i love these things

ok, here goes

1. The Killer - for committing murder
2. The Ferryman - for refusing to put aside monetary concerns to save a life
3. Mary - She should not have gone back to the bridge to meet her killer, she gave up and gave in to despair apparently
4. Husband - not satisfying your wife? tsk tsk!
5. Lover - Who knows the dynamics of his and Mary's relationship? Maybe he didn't believe her, or maybe she was Madame Bovary incarnate or something, who knows.