Director Joe Berlinger says when it comes to serial killer John Wayne Gacy, a big part of his horrific rampage had to do with self-hatred and his inability to deal with his sexuality.
The Oscar-nominated filmmaker joined us on "TMZ Live" Monday to talk about digging into the mind of the notorious Illinois serial killer for his new Netflix docuseries, "Conversations With a Killer: The John Wayne Gacy Tapes" ... and, as you might imagine, it's a frightening ride.
The film explores what made Gacy -- a birthday clown by day -- tick during his reign of terror in the 1970s. Berlinger says listening to Gacy's conversations with attorneys and cops ... showed how much the mad man blamed his victims.
He says the killings had a lot to do with Gacy's self-hatred, and inability to deal with his sexuality. As for why it took so long to catch him, Joe says society's prevailing attitudes toward marginalized groups, like the gay community, were a major factor.
On a personal note ... Berlinger admits he struggles to leave his work at home. He's been delving into the minds of murderers for decades now, and he told us why his Oscar-nominated doc, "Paradise Lost" -- about the 1996 slayings of 3 West Memphis boys -- was particularly difficult.
Joe says, "I was trying to have a tender moment with my new child, and I just kept flashing on the worst images of what happened to these children".
Ultimately, he's been forced to master the art of compartmentalizing, and told us one tool he uses.