why call the cops ????

She's crazy!!!! or in more PC terms has multiple personalities. The problem people have with this film stems from them thinking Marie is a normal person who is just obsessive. She's not.

Remember she is telling the story as if her crazy split personality actually exist. She really thinks she is calling the cops on a KILLER and I think she kills Jimmy because he sees something that gives it away.

The bottom line is that she is batsh*t crazy and is telling the story. Therefore we don't even know if any of it is true.

She called the cops because she wasn't even aware that she was the one doing all the killings. She was crazy. I guess you could say that she had a super split personality. And the reason she killed Jimmy was because he spotted blood on her hand. That was her way of covering up her tracks and getting rid of a witness...I guess. But then again, her mental state had collapsed, all sense of reality was gone, and she was going on a brutal killing spree. There's not much logic behind the death of Jimmy. He was just in the wrong place, at the wrong time.