Titles are my favorite! I usually try to pick a title based on what I think the most important aspect of the story is as well or play on character names. Two that I've recently come up with are "Roses Are Red"--my MC's name is Violet (who is called Flower by the girl she falls for) and it's about her falling in love for the first time, and "Chasing Jess"--my MC, Chase, tries to romance the girl of her dreams, Jess (see what I did there?!). So, think about what a major aspect of your story is. If it's generally just about the life of a serial killer you could try something like "Living and Killing" or "Deadly Woman". Those probably aren't great but maybe a place to start?