Gardner, 31, who reached a plea deal last month that spared him the death penalty, breathed heavily and cried at times during emotional statements by the girls' parents and Moncayo before Superior Court Judge David Danielsen pronounced the sentence.
He raised his head when Kelly King, Chelsea's mother, demanded that she look at him. He refused when she asked him a second time.
"Why am I not surprised?" she said.
Gardner, who did not speak at the hearing, cried during a video of Amber's life. He showed a flash of anger when Moncayo asked about his smashed nose, veering from her prepared remarks.
Moncayo said she came to ask "to remove this man from our world, to make us a little safer by locking him up permanently and to finally free us from the nightmare he created."
Gardner's crimes have sparked a far-reaching review of how California deals with sex predators, a campaign that advocates hope to take to Washington and state capitals.
Chelsea's parents are leading a campaign for "Chelsea's Law" to allow life sentences for some convicted child molesters in California and lifetime electronic monitoring of others. The bill, which cleared its first legislative committee last month, would also ban sex offenders from parks.
The Kings on Friday also blamed Gardner's mother, Catherine Osborn, for failing to stop her son, who served five years of a six-year prison sentence for molesting a 13-year-old neighbor in 2000.
Brent King, turning to address her in her front-row seat, said she would always bear "our pain on your soul."
"She knew what you were capable of and did nothing," Kelly King said. "She lacked the humanity and human decency to do the right thing ... Your mother will always be intertwined with your horrific crime because she did nothing."
Osborn dabbed her face with tissue as Carrie McGonigle, Amber's mother, described her devastating loss. McGonigle said she often obsessed about her daughter's final moments.
"Was she scared? Was she calling my name? No one can appreciate the horror that is my life until they can appreciate the joy that was my Amber," McGonigle said.
Amid their anger, the girls' parents spoke lovingly of their daughters on Friday.
Brent King said he loved changing Chelsea's diapers and, later on, talking with her about global issues, competition, life's pressures and her dreams. They joked about God's sense of humor in creating the platypus.
King said it was impossible to fathom how bittersweet it was to receive acceptance letters from all 11 colleges to which his daughter applied.
"Chelsea was everything this man was not," he said. "She was as good as this man is evil."
Calls to stiffen penalties for child sex offenders began almost the moment Gardner was arrested Feb. 28, three days after he attacked Chelsea on an afternoon run in San Diego, strangled her, and buried her in a shallow, lakeside grave.
Gardner faced a maximum of nearly 11 years in prison for molesting his neighbor in 2000, but prosecutors called for six years. A court-appointed psychiatrist urged the maximum sentence allowed by law. He said in court documents that Gardner was a "continued danger to underage girls" and "an extremely poor candidate" for treatment.
Maurice Dubois, Amber's father, read from by psychiatrist Matthew Carroll report during his statement in court Friday.
He likened his daughter's killer to a mountain lion whose instincts are to stalk and attack. If the zookeeper frees the lion from captivity, he asked, who is responsible for the killings that come after?
"It's obvious the legal system failed us with all of the missed opportunities that ultimately allowed this monster to stalk our streets and harm our loved ones," he said.
The case has also put California's parole system under the microscope, and Gov. Arnold Schwarzenegger has ordered a state board to review the system.
Gardner lived little more than a football field's length from a San Diego preschool for at least 16 months while on parole from 2005 to 2008. That violated a condition of parole that prohibited him from living within a half-mile of a school.
A corrections department official let him stay until his lease expired in 2006 but no one noticed he was still living there until a year later. The parole board could have sent him back to prison but kept him on parole, where he had six other less serious potential violations.
The discovery of Chelsea's semen-stained clothing during a massive search quickly led authorities to Gardner. Days later, he led investigators to Amber's remains in a remote, mountainous area north of San Diego.
The investigation into Amber's disappearance had gone nowhere since the Future Farmers of America member disappeared walking to school in suburban Escondido in February 2009.
Gardner led authorities to Amber's remains on condition that the information not be used in court. Investigators were unable to independently link him to the crime, and his guilty plea to that murder was a big reason why the death penalty was dropped.