The quest to understand what makes serial killers tick is a whole industry.

But what about someone like Elmer Wayne Henley Jr. ? While he's a convicted serial killer, it's impossible to know if he ever would have committed murder on his own if he hadn't crossed paths with "Candy Man" Dean Corll , who tortured and murdered at least 27 boys and young men in the Houston area between 1970 and 1973.

"I'm willing to accept that's a period of my life I may never have an understanding of," Henley told Dr. Katherine Ramsland in a prison interview heard in the new Investigation Discovery documentary The Serial Killer's Apprentice , premiering Aug. 17. "I have never been allowed to further that storyline."

But Ramsland wanted to know more about how Henley, who was still a teenager hims

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