SAN DIEGO - With two teary-eyed mothers looking on, convicted sex offender John Albert Gardner pleaded guilty Friday to raping and murdering their teenage daughters -- a surprising turn in the duel tragedies that fueled calls for California to toughen its sexual predator laws.

Sobs pierced the packed courtroom as Gardner, 31, admitted kidnapping, raping and stabbing 14-year-old Amber Dubois, and dragging 17-year-old Chelsea King to a remote area where he raped, strangled and buried her.

As part of the plea deal, he also admitted trying to rape a female jogger last year in San Diego who managed to escape.

Gardner, wearing a dark blue jail jumpsuit with his shackled arms hanging at his sides, said nothing but "yes" repeatedly as the judge asked him for his pleas.

He faces life in prison without parole and has waived his right to appeal.

Parents Brent and Kelly King, and Maurice Dubois and Carrie McGonigle were in the courtroom to hear the admissions. Kelly King and McGonigle were teary-eyed throughout the proceeding.

The two families agreed to accept Gardner's plea deal with prosecutors, who said they would not seek the death penalty if he pleaded guilty to both murders.

"There's nothing satisfying about this moment. It is only one more unbearably painful day that we will have to carry in our memory as long as we live," Brent King said after the hearing. "Accepting this plea has been an extremely difficult decision," added District Attorney Bonnie Dumanis. "We have the evidence to pursue a murder charge against the defendant for Chelsea's murder, but not for Amber's murder."

Gardner served five years in prison after pleading guilty in 2000 to molesting a 13-year-old neighbor girl. Records show he later violated parole by moving too close to a school but was allowed to remain free.

His treatment has led to calls to strengthen California's already stringent laws on sex predators.

Chelsea King disappeared Feb. 25 during an afternoon run in a San Diego park. Her body was discovered five days later in a shallow lakeside grave after a massive search for the straight-A student and member of the Poway High School cross-country team.

Gardner was arrested three days after she disappeared and initially pleaded not guilty to her killing. Prosecutors said he was linked to the crime by DNA found on her clothing.

Two days after authorities charged Gardner, he agreed to lead them to the bones of Amber if they did not go public with the information or use it against him in court.

Officials, however, retained the ability to use any evidence obtained from the crime scene to build their case.

"This was a somber decision," Dumanis said. "To end the anguish of the unknown for the Dubois family and to bring Amber home, we agreed."

Escondido police and crime lab technicians worked round-the-clock to find evidence linking Gardner to her murder, but Dumanis said they did not succeed.

Amber had vanished Feb. 13, 2009 on her way to purchase a lamb she was going to raise for Future Farmers of America.

Brent King said his family agreed to the plea deal to spare their 13-year-old son the drama of a protracted trial and appeals process, which prosecutors said could drag on for decades.

"The decision whether to give our blessing to the district attorney's proposal was torturous," he said. "While our unequivocal first choice is the death penalty, we acknowledge that in California that penalty has become an empty promise."

The Kings also wanted to help the grieving family of Dubois.

"The Dubois family has been through unthinkable hell the past 14 months. We couldn't imagine the confession to Amber's murder never seeing the light of day, leaving an eternal question mark," he said.

The King family has traveled to Sacramento in support of a proposed "Chelsea's Law" that would send some child molesters to prison for life after a first conviction and monitor others with tracking technology until they die.

Defense attorneys left the courtroom without talking to reporters. Gardner is expected to be sentenced June 1.