Gardner is headed to prison for life, but in a news conference Monday, members of the three-county John Gardner task force said their work is not done.
"The Gardner task force has not been disbanded," said prosecutor Kristen Spieler. "So there are still continuing investigations to see if he's connected to any other unsolved crimes."
Gardner spoke to investigators after his sentencing Friday. They say he admitted involvement in other attacks, but didn't implicate himself in more murders. Detectives are not taking him at his word.
"We're looking at him actually for all missing persons' cases," said Lt. Dennis Brugos with the San Diego County Sheriff's Office."For females in the range of early teens through early twenties, from three different counties."
Gardner made a plea deal last month, avoiding the death penalty by admitting he raped and killed King and Dubois. He also admitted to trying to rape Candice Moncayo in a San Diego park.
"It's been 6 months since John Gardner attacked me and some mornings I still wake up screaming," she said at his sentencing Friday.
Gardner led investigators to Dubois' remains in a remote area of San Diego after King's body was discovered in a watery grave. He helped investigators on the condition the information not be used in court.
"I mean, I was aware of what I was doing, and I could not stop myself," he said of his crimes. "I was in a major rage."
Gardner teared up in court when he saw a video tribute to one of his victims. He looked down when the girls' parents confronted him. But his demeanor was much different during a jailhouse interview when a reporter asked him about his history.
"Are there other victims?" she asked.
"Ha ha ha," he laughed. "Good try."
If there are more victims, the Gardner task force hopes to find them. And if they do, John Gardner's next stop could be death row.