Abusive boyfriend character needs to be murdered...

I'm working on an installment of a mystery series. The main character, Kat, has been in a previous abusive relationship which she escaped. She fell in love with Peter, who had been abused as a child (bonding moment there), and the two of them get married (or try to).

This is the story of their attempted marriage. They get to the ceremony, but so does the abusive boyfriend (Jeremy). Kat runs out of the church at the sight of him and disappears. Jeremy causes commotion with everyone else at the ceremony and takes off to find Kat. Everyone there hates him for what he did to her in the past.

Jeremy gets hold of Kat's wedding dress and puts it on (presumably when she ditched it to change into street clothes -- haven't worked out completely), then gets into Peter's hotel room, tries to kill him. He gets spooked by someone coming to the rescue and jumps out the window, leaving a bit of the dress behind.

Peter vows to find Kat and the person who tried to kill him (because he's convinced they're not the same person) -- but then Jeremy turns up dead.

I can't figure out if it's more satisfying if Kat kills him (as revenge), or if everyone would be expecting that and wouldn't be much of a mystery. But if she doesn't do it, who does? And why would that person's reasoning be more interesting than if Kat did it?

This story is in the early brainstorming stage, so I'm sorry the details are shoddy.
Thanks for reading!!

You are asking us to make a dicision that only you can make. Once you've decided we can certainly suggest what we think are piculliar methodologies to get the job done.

How much do you want Jeremy to suffer?

Do you want it to be premeditated?

Abusive people, are abusive... Is it really that hard to believe that someone else with a history with him had enough? Or that he didn't simply pick the wrong person to attempt to abuse? You could set it up to look like Kat did it. And the police jump at Kat doing it and fail to really do their job. The Police / DA bring pressure to bear on Kat in an attempt to close the case...

It is only at the end of the book we learn The Ex was trying to pick up a new girlfriend, only she was already another abusive guy's property who took a strong objection to him trying to move in on his woman and so killed him!