Investigators could soon discover whether infamous serial killer John Wayne Gacy killed more victims.

The Cook County, Illinois Sheriff’s Office says that Gacy’s DNA was recently added to CODIS, a national DNA database.

Gacy was found guilty of raping and killing 33 boys and young men in 1980. Twenty-eight of the bodies were discovered beneath his home. He was executed by lethal injection in 1994.

Cook County investigator Jason Moran has led the efforts to put the executed serial killer’s blood samples into CODIS, in hopes that other victims can be found.

Once the sample is in the database, investigators are able to cross-reference the serial killer’s DNA with those found in cold cases.

Moran ran into some legal issues in his efforts. A law, which was passed in 2002, stated that anyone incarcerated in the Illinois Department of Corrections for a life or death sentence has to provide a DNA sample.

However, since Gacy was executed before 2002, his DNA could not be legally put into the database.

Moran eventually discovered that any homicide victim’s blood could be submitted, no matter when they were killed. Since, a killer’s death is ruled a homicide when they are executed, Moran was able to put Gacy’s DNA sample into CODIS.

Three executed killers' DNA have been put into CODIS so far. No matches have been made.