The killer is among the world’s most notorious mass-murderers: John Wayne Gacy, the amateur clown convicted and executed for the grisly murders of 33 young men in the 1970s.

But at least eight of his victims, who were buried around Gacy’s Chicago home and in a nearby river, were never identified. Now, detectives have exhumed their remains in the hope that advances in DNA can identify them and, Cook County Sheriff Tom Dart said, “close the book once and for all on John Wayne Gacy.”

The jawbones of the unidentified victims were sent to a lab at the University of North Texas, which developed DNA profiles for four of them. The bodies of the other four were then exhumed in order to get fuller DNA profiles. “If you didn’t have dental records back then, there wasn’t much that could be done,” Dart said.

Now the sheriff is asking anyone to come forward if they know of boys or young men who disappeared between 1970 and 1978. “We’re looking at a pretty broad group to come forward to try to help us,” Dart said, encouraging relatives whose missing family members fit the profile to submit to saliva tests so a DNA match can be established.

The new attempt to identify Gacy’s victims follows a decades-long quest by a mother who never believed her missing son was among them. Earlier this month, lawyers for Sheri Marino, 67, convinced a judge to order the exhumation of her son, Michael, who had been reported missing along with one of his friends, Kenneth Parker, on the same day in 1976.

Judge Rita Nowak noted discrepancies between the boy’s medical records and autopsy reports, including a tooth – a permanent molar – that his mother insists he did not have. The DNA testing on his body is expected to take several months. “With DNA now we have so much more we can do,” Dart said.

He said he hopes the new testing will eventually provide answers for Sheri Marino and other families who have never known, for certain, whether their missing sons were among Gacy’s victims.