An investigation into the case of John Wayne Gacy, who forty years ago murdered over 30 men in Illinois, has helped solve a cold case for an unrelated murder committed in 1978, authorities told the Associated Press Wednesday.

Investigators are still continuing their efforts to identify Gacy's victims, whom he strangled to death in the Chicago-area during the '70s, by asking possible family members to submit DNA. In the meantime, the skeleton of a man who lived near Gacy and disappeared in July 1978 remained sitting in a lab. Thanks to a coincidence, where one family's DNA and the remains ended up at the same lab, the killer- who is not Gacy- and the man have been identified.

The remains belong to Edward Beaudion, 22, who was last seen after he dropped a friend off at her house on July 23, 1978. His skeleton, with the exception of the skull, was found by hikers in a forest preserve in 2008.

"I always thought he was killed but you still aren't sure until you get the proof," Louis Beaudion, Edward Beaudion's father, told the AP.

The discovery was put in motion when eight of Gacy's unidentified victims were exhumed for testing. Authorities asked those who had relatives disappear in the '70s, including Edward's family, to submit DNA.

Edward's sister, Ruth Rodriguez, complied.

"I didn't think Gacy killed him but we figured we'd go ahead and try," she told the AP.

Meanwhile, the lab that had Edward's still unidentified remains was in the process of organizing its stock of bodies, some of which were carelessly placed in boxes. Edward's remains ended up being sent to the same lab where his family's DNA was tested.

The lab discovered a "genetic association" between the remains and DNA from the Beaudion family, the AP reported.

The identification, which exonerated Gacy as the killer, led to the suspect originally accused of murdering Edward, a man from Missouri named Jerry Jackson. But authorities may never be able to find out if Jackson is the real killer. Jackson died in 2013 at the age of 62, the AP reported. Gacy was executed in 1994.

But Edward's family is still grateful for the closure. Detective Jason Moran was there when Edward's father was shown the place his son's remains were found.

"This guy, 36 years after his son is killed, he's crying like he went missing yesterday and then he grabbed my arm and said, 'Thank you,' " Moran told the AP.