CHICAGO (CNN) -- Laura O'Leary was a teenager when her 19-year-old brother disappeared in 1976, but she long suspected what had happened to him. She just couldn't prove it.
More than three decades later, DNA tests confirmed her suspicions, authorities in Chicago announced Tuesday. William George "Bill" Bundy fell victim to serial killer John Wayne Gacy, the "killer clown" who murdered nearly three dozen young men and boys before police discovered the crude cemetery beneath his home in 1978.
Bundy's remains had been identified only as "Victim 19" until mid-November, when genetic testing confirmed his identity, Cook County Sheriff Thomas Dart said. Bundy is the first of eight long-nameless Gacy victims to be identified in an effort launched in October.
"I remember him leaving that one night, saying he was going to go to a party," O'Leary told reporters Tuesday. "And that was the last time I saw him."
Bundy had been a diver and gymnast in high school, said O'Leary, who was 17 at the time he disappeared.
"All my girlfriends wanted to date him. They didn't come over for me, only for him," she said.
Police began hauling bodies out of Gacy's crawl space in December 1978. O'Leary said she began to think her brother's was one of them after she learned that Gacy had been a construction contractor. Bundy had just gotten a job with a contractor and had talked about how he was learning to be an electrician.
"My mother was pretty much in denial, but I made her go to the dentist," O'Leary said. But their dentist had retired, and his records had been destroyed.
"Without DNA back then, there was nothing I could really do," she said. But DNA samples from O'Leary and her brother, Robert Bundy, matched the remains, Dart said. Both their parents are now deceased, O'Leary said.
Gacy, a part-time party clown, was put to death in 1994 for the killings of 33 boys and young men between 1972 and 1978. "Victim 19" was believed to have been between 17 and 21 years old and between 5-foot-1 and 5-foot-6, investigators said.
Bundy, at 5-foot-5, was the shortest of Gacy's victims and in the same age range, Dart said. In addition to the DNA testing, Dart said a friend of Bundy's also came forward to describe him showing off a wallet full of cash from his new construction job. Gacy had used the promise of work as one way of luring his victims, along with posing as a police officer or picking up runaways.
O'Leary said her family filed a missing-person report when Bundy failed to come home in 1976, but "it wasn't handled aggressively." Dart said the original report has not yet been located.
At the time, "missing-persons cases were not given very much thought and certainly were not professionally handled," Dart acknowledged.
Investigators are still pursuing 80 other possible leads regarding the seven remaining unidentified victims, he said. While Bundy's family finally knows what happened to him, four other families who have stepped forward as possible relatives of other victims have been ruled out by DNA tests.
"There's nothing fortunate about being a victim in this case, but these families were looking for closure, and we were unable to provide that," he said.
A sample of Gacy's blood discovered among the case evidence has been submitted to a Justice Department database of DNA samples, but Dart said his office had no indication that Gacy had victims in other states.
"We're not trying to lead people to believe we have any specific leads on anything in that nature,'' he said. "It is a tool that is commonly used by law enforcement, and it is something that needs to be done."