Investigators have used DNA evidence to identify one of the seven remaining unknown victims of John Wayne Gacy, a 1970s serial killer who raped and murdered dozens of teenage boys and young men and was dubbed “the killer clown” by the news media, the authorities said today.

The Cook County Sheriff’s Department in Illinois said that the newly identified victim was James Byron Haakenson, 16, who ran away from his home in St. Paul in the summer of 1976. The police found his body and 26 others in the crawl space beneath Gacy’s home in December 1978.

Gacy was among the most prolific serial killers in U.S. history. From 1972 to 1978, he lured or forced 33 teenage boys and young men — some of whom he employed in his construction business — to his home in suburban Chicago, where he murdered them. He sexually assaulted most of his victims as he tortured them to death and buried all but six of them beneath his house.

Neighbors in Norwood Park Township, Illinois, knew Gacy for his appearances at children’s parties where he performed as “Pogo the Clown,” a character he later painted or sketched numerous times while in prison.

Gacy was convicted in 1980 of killing 33 people and was executed in 1994. But identifying the remains of his victims has been a decades-long process aided in recent years by advances in forensic technology and the use of DNA evidence.

The police notified Haakenson’s family Monday that his remains had been identified.

“It’s not every day you heard this: A monster murdered your brother,” his sister, Lorie Sisterman, told a CBS affiliate in Chicago. “It’s just not an everyday, normal conversation that you have with a detective from a different state who tells you this awful news.”

Haakenson’s family last heard from him Aug. 5, 1976, when he called home and told his mother that he was in Chicago, the department said. Investigators believe he crossed paths with Gacy soon after that call.

His body was found in Gacy’s crawl space in December 1978 in a makeshift grave alongside two others. One of those bodies was identified at the time as Rick Johnston, who was last seen Aug. 6, 1976.

The department said it believed Gacy murdered Haakenson and Johnston either at or around the same time based on the last time they were seen and their relative positions in the crawl space. Investigators have not been able to identify the third body in that grave, which is classified as Victim No. 26.

Thomas J. Dart, the Cook County sheriff, reopened the investigation to identify the remaining victims in 2011, when there were eight whose identities were not known. Since then, investigators have identified one other victim: William Bundy, 19, who disappeared in October 1976.

The department said Haakenson’s mother tried to determine in 1979 if her son’s body was among those found under Gacy’s house, but dental records, which were the primary means of identification at the time, were unavailable. She is no longer alive, the department said.

The authorities identified Haakenson’s remains by requesting DNA samples from two of his siblings and submitting them to the University of North Texas Center for Human Identification. They also reviewed the original missing person’s report filed by Haakenson’s family, information from the Social Security Administration and post-mortem reports.

Gacy’s unidentified victims were buried in 1981 under tombstones inscribed with the words “We Are Remembered.” The sheriff’s department said its investigation into the identities of the six remaining unknown victims was continuing.

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