CHICAGO – Detectives have long wondered what secrets serial killer John Wayne Gacy and other condemned murderers took to the grave when they were executed – particularly whether they had other unknown victims.

Now, in a game of scientific catch-up, the Cook County Sheriff’s Department is trying to find out by entering the killers’ DNA profiles into a national database shared with other law-enforcement agencies. The move is based on an ironic legal distinction: The men were technically listed as homicide victims themselves because they were put to death by the state.

Authorities hope to find DNA matches from blood, semen, hair or skin under victims’ fingernails that link the long-dead killers to the coldest of cold cases. And they want investigators in other states to follow suit and submit the DNA of their own executed inmates or from decades-old crime scenes.