Serial Killer of the FBI

If you can't beat your enemy, then join them. In the FBI's case, if you can't beat them then give them a job. The BAU is about to get a new expert to help them on their cases, a man who made it his mission to hunt monsters and put them in the ground. A Serial Killer is now going to join the FBI in hunting the worst of the worst. Will include the two spin-off series of the original.