The senator
Kinda felt bad about him killing himself. Aside from infidelity, he hadn't done anything wrong. Basically the protagonists unnecessarily caused his death.
shareHe unnecessarily caused his death - and in the oldest Hollywood cliche where a man opens his desk drawer and you know he's going to pull out a gun and blow his brains out. Goes back to "The Fountainhead" in 1949, at least. Probably there are even older examples.
shareHe thought he had killed the girl and was going to be exposed for that, facing perhaps prison and at least a public scandal and the end of his political career.
shareyeah he thought that , but he hadnt - like the OP said.
Then for some reason our hero cops faxed him some pictures of what he thought he knew , so he killed himself