It's being used as a technicality.
While the state does send to the FBI's Combined DNA Index System the profiles of homicide victims no matter when they were killed, 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," O'Neil said
Yes, technically that’s true, they were killed by another person and are therefore homicides in the cause of death category. But there really should be a qualifier in the case of executed persons, since this has obviously interfered with the collecting of information, including police and, I would assume, statistical information.