That was only the first obstacle.
The state sends to the FBI's Combined DNA Index System the profiles of homicide victims no matter when they were killed. But it will only send the profiles of known felons if they were convicted since a new state law was enacted about a decade ago that allowed them to be included, Moran said.
That meant the profile of Gacy, who received a lethal injection in 1994, and the profiles of other executed inmates could not qualify for the database under the felon provision. They could, however, qualify as people who died by homicide.
"They're homicides because the state intended to take the inmate's life," said Patrick O'Neil, the Will County coroner.
Last year, authorities in Florida created a DNA profile from the blood of executed serial killer Ted Bundy in an attempt to link him to other murders. But the law there allows profiles of convicted felons to be uploaded into the database as well as some profiles of people arrested on felony charges.
Florida officials said they don't know of any law-enforcement agency reaching back into history the way Cook County's sheriff's office is.
"We haven't had any initiative where we are going back to executed offenders and asking for their samples," said David Coffman, director of the Florida Department of Law Enforcement's laboratory system. "I think it's an innovative approach."
O'Neil said he is looking for blood samples for the rest of the 12 condemned inmates executed between 1977 and 2000. So far, DNA profiles have been completed on the blood of Gacy and two others.
Among the other executed inmates whose blood was submitted for testing was Lloyd Wayne Hampton, a drifter executed in 1998. Hampton's long list of crimes included some outside the state — one conviction was for the torture of a woman in California. But shortly before he was put to death, he claimed to have committed additional murders but never provided details.
So far, no computer searches have linked Gacy or the others to other crimes. But Moran and O'Neil suspect there are investigators who are holding aging DNA evidence that could help solve them.
That is what happened during the investigation into the 1993 slayings of seven people at a suburban Chicago restaurant, during which an evidence technician collected and stored a half-eaten chicken dinner as part of the evidence. There was no way to test it for DNA at the time, but when the technology did become available, the dinner was tested and revealed the identity of one of two men ultimately convicted in the slayings.
Moran wants investigators in other states to know that Gacy's blood is now available for analysis in their unsolved murders. He hopes those jurisdictions will, in turn, submit DNA profiles of their own executed inmates.
"That is part of the DNA system that's not being tapped into," he said.