Angel Killer is a standalone novel by author Andrew Mayne. The book follows FBI Special Agent Jessica Blackwood as she works with other agencies to chase a killer known only as the Warlock. The Warlock is a serial of extreme proportions. He is committing crimes that just seem impossible and that is why Blackwood has been brought in- to use her magician's skills to try and understand how and why the Warlock is committing his crimes.
The idea is a strange one. I can see this being turned into a film it is that good.