He’s been dead for nearly 20 years, but serial killer John Wayne Gacy may be helping a Chicago sheriff’s office tie more murders to him in the form of his DNA.

At least 33 murders have been linked to Gacy, all either teenage boys or young men. The majority of the serial killer’s victims were buried in a crawl space in his Cook County home, while others were dumped into a nearby river.

Now officials from the Cook County Sheriff’s Office are trying to link Gacy to more murders by using his DNA from his blood and entering it in a national database, the Associated Press reported. The office is able to do that because Gacy was listed as a homicide victim when he was executed via lethal injection in 1994.

Gacy is one of several executed men whose DNA is being used to determine if they have more victims than is currently believed.

"You just know some of these guys did other murders" Cook County Sheriff’s Office Det. Jason Moran told the AP.

The testing of Gacy’s DNA began over the summer, and was spurred after Cook County Sheriff Tom Dart exhumed the remains of unknown Gacy victims and created a database to see if the remains matched missing teens or young men in the 1970s, when the serial killer began his spree. The effort identified a previously unknown Gacy victim,

Dart realized he could work backwards and use Gacy’s DNA to find other unknown victims.

The sheriff’s office has long wondered if there were other victims besides the ones found in the crawl space in Gacy’s home or the nearby river.

Moran says Gacy’s travel patterns may indicate that there are more victims.

"He traveled a lot," Moran told the AP.  "Even though we don't have any information he committed crimes elsewhere, the sheriff asked if you could put it past such an evil person."

Before he was caught, Gacy was an unassuming member of his community. He had a job as a children’s clown and was also a Democratic precinct captain.