Xavier was exhausted after investigating the link between the Heartless Butcher and the supernatural world. He visited the holding cell where the screaming man was held and looked into his memories.
The delve into the serial killer's mind was unpleasant as it always was when dealing with perverted brains. It was like sinking a hand into the most disgusting sludge. The stink always clung for a while.
After the mind dive, Xavier discovered that the middle-aged man did have something to do with witches. His ritualistic kills were used to harness the life force of the young girls for the purpose of black magic.
However, the Heartless Butcher was not a victim. He was a cold psychopath who started killing way before the witches found him and made a deal to protect him from discovery as long as he let them siphon the life magic.