U.S. police probe possibility serial killer John Wayne Gacy may have struck in Canada

They called John Wayne Gacy the Killer Clown and almost two decades after he was executed, police are investigating whether the infamous serial killer may have struck in Canada.

Gacy, who lived in the Chicago suburb of Norwood Park, was convicted of murdering 33 young men and teen boys over a six-year period in the 1970s. The pudgy building contractor earned his creepy nickname because he sometimes performed as a clown at children's parties.

Police arrested Gacy in December 1978 after connecting him with the disappearance of 15-year-old Robert Piest, a drugstore stock boy seen going to Gacy's car outside the shop.

A search of his home turned up 27 bodies stuffed in the crawlspace under his house and two more in the back yard. Four more bodies, including Piest's, were found in the Des Plaines River.

Many of Gacy's victims were male prostitutes and in his confession he said he sometimes impersonated an undercover police officer, handcuffing his victims and taking them to his home. He also sometimes lured victims to his home "with promises of construction jobs, drugs and alcohol," or offering money for sex, according to police. Once there, they were sexually assaulted and strangled.

Gacy was executed in 1994.

Now police are trying use DNA to trace eight of Gacy's victims who were never identified. Detectives secretly exhumed the bodies earlier this year.

As part of their cold-case investigation, detectives with the Cook County Sheriff's Office went through boxes of evidence from the initial investigation. They turned up airline ticket stubs that show Gacy traveled to Canada and 13 U.S. states between 1972 and his arrest in 1978, Randy Boswell of Postmedia News reports.

Sheriff Tom Dart said Gacy's trips coincide with the disappearances of at least 27 young men in several states and Ontario.

Dozens of families, including one from Canada, have responded to Dart's request for information that might link Gacy to their missing loved ones.

"How, conceivably, can you think of a guy that does these horrific acts, but yet he turns it off when he leaves town?" Dart told NBC News. "You would think the opposite. He's leaving town, he's even more free because people don't know who he is. He can move around even better."

Dart said as many as five officers will work on the revived leads.