Hey could someone please help me with figuring out my antagonist's motive?

So near the beginning of my story, the antagonist (Chase) kidnaps the protagonist (Genevieve). As this story is still in the early stages, I haven't really developed this plot point yet. I'm thinking it could have something to do with Genevieve's godfather, Jasper.

Jasper is a police detective who, at the beginning of the story, has been working for months to catch a serial killer (Chase) and has finally caught him. However, Chase escapes from his cell and kidnaps Genevieve. I still don't have a motive for Chase, though.

Any help would be much appreciated!

Try to flesh out Chase - why is he killing people? What does he gain from doing so? It does not need to be the actually killing part but could be the 'hunt', or the fact that he outsmarts the police. He could kidnap Genevieve simply because Jasper is the one guy that he couldn't outsmart. What if it was actually Genevieve that found out his pattern and relayed it to her godfather - unbeknownst to Chase.
It all depends on how involved you want. I would try and figure out more about your characters - what their backgrounds are, education etc could all play a major part in their choices.
Hope this helps!

Thankyou so much!