CHICAGO (CBS) — The possibility that more victims of John Wayne Gacy could be buried on the Northwest Side has prompted the Cook County sheriff to push once again for a dig on private property.

As WBBM Newsradio’s Steve Miller reports, Sheriff Tom Dart has already tried to get a dig authorized at Miami and Elston avenues, where John Wayne Gacy worked as a maintenance man.

LISTEN: WBBM Newsradio’s Steve Miller reports

RELATED: CBS 2 Vault: John Wayne Gacy Speaks

But the Cook County State’s Attorney’s office turned him down.

“I’ll be honest with you – with the original information we had provided, to me it was more of a 50-50 call,” Dart said.

Dart still wants the search warrant, and he’s putting a supplemental request together.

“I’ve read, I think, four more affidavits from people that bring new evidence or more substance to existing evidence as to why it would be a good thing to do,” he said.

Dart says he will get the new request to the State’s Attorney in the next week or two.

A 1998 dig on the property turned up nothing.

But Dart says he thinks with this new information, finding something is more likely.

“It’s just led me to believe that, given the enormity of what this monster did, how do you not just run it out?” he said.

Dart says he’ll be sending a new request for a search warrant to State’s Attorney Anita Alvarez in the next week or two.

Gacy, an ex-convict with a history of sodomy convictions, worked as a contractor on Chicago’s Northwest Side and northwest suburbs in the years immediately preceding his arrest. He was a Democratic precinct captain and worked as a clown at children’s parties.

Gacy was arrested in December 1978, after 29 bodies were found in a crawlspace under his house at 8213 W. Summerdale Ave. in unincorporated Norwood Park Township. Four more bodies were found in the Des Plaines River.

After barely two hours’ deliberation in 1979, Gacy was found guilty of 33 counts of murder.

Gacy was executed on May 10, 1994. Notoriously, his last words were, “Kiss my ass.”

Last year, a positive DNA match identified one previously unknown Gacy victim – William George Bundy, who was 19 when he disappeared in 1976.