Serial killer John Wayne Gacy had a dual personality which led him to kill 33 young men and boys in the Chicago area, a retired journalism professor who interviewed Gacy on death row says.

Harlan H. Mendenhall, an SIUC emeritus professor, is the author of the book, Fall of the House of Gacy, which he wrote after spending 570 hours in a seven-year period in the 1980s interviewing Gacy before the man was executed last year. Mendenhall signed copies of his book, which focuses on Gacy’s personality instead of the murders, in the Communications Building Thursday.

Gacy had a dual personality but kept it well hidden from the rest of the world, Mendenhall said. He said Gacy’s dual personality was always there, but Gacy did not realize it, or his homosexuality, until he had an affair with a 15-year-old boy in Iowa.

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Mendenhall said the boy blackmailed Gacy for money for about six weeks until Gacy could no longer afford to pay the boy. Gacy told the boy to tell his father of the affair, and the boy did, Mendenhall said. Gacy was arrested and went to prison in Iowa.

From there on, John was the B personality and was out to get anybody he could, Mendenhall said. He was angry at all boys from 15 to 18 because the boy had ruined his life. That’s why he killed them.

After Gacy went to prison, he lost complete control of his dual personality, Mendenhall said. He said Gacy was able to cover up the dual personality from the rest of the world and himself.

Even towards the end, he was saying he was a nice guy, Mendenhall said.

Mendenhall said there was always a prison guard present when he interviewed Gacy in a 10 foot by 10 foot prison cell. He said Gacy had to wear hand and ankle cuffs during the one-hour interviews.

During the interviews, Gacy talked about how his father had abused him, starting when Gacy was 3-years-old, Mendenhall said. Mendenhall also interviewed Gacy’s mother for 50 hours. He said Gacy’s mother, who was also abused by Gacy’s father, was afraid to report the abuse to the police.

John was in the hospital once for 29 days after his father kicked him down some stairs, Mendenhall said. Mama Gacy said she would never forgive herself for not turning him (her husband) into the police.

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While he was interviewing Gacy, Mendenhall said there was always an evil presence in the room with them. He said Gacy claimed he was not evil and could hold back the evil personality, except during one of his tirades.

He didn’t blow up or get violent but three or four times in all the years I interviewed him.

He called me at the end and said I was the only friend he had and I thank you,’ he said. I don’t know if he meant that somebody saw what he did and still talked to him.

Gacy asked Mendenhall to go to his execution, but Mendenhall said he could not do that.

I said no’ because I could not stand to see another person killed, he said. I felt sorry for him, even at the end.

Mendenhall said he eventually agreed to go to the execution but still could not do it. He said Mary Tupper, who graduated SIU in 1974, helped him with the book and took his place at the execution.

John never did know the difference, Mendenhall said.

Tupper said she was not allowed to see the execution because she did not have the clearance, but she was allowed on the grounds.

She said Gacy sent an autographed picture to she and her son Brian. She said the picture read:To my good friends Mary and Brian.