The sentencing followed an hour of emotional statements from the girls' families. At times Gardner appeared emotionally shaken and wept as videos were shown in the court room.
"Chelsea was a sweet, loving and innocent soul who could not have fathomed the wretched piece of evil that ended her life that day," said Chelsea's mother, Kelly King.
Gardner, 31, kept his head down most of the hearing and only looked up when demanded by Chelsea King's mother.
"You've taken my daughter and my best friend," Amber's mother Carrie McGonigle said to Gardner. "I would have laid down my life for Amber."
Authorities arrested Gardner earlier this year after finding semen-stained clothing during a massive search for Chelsea. Gardner then lead investigators to Amber's remains after King's body was discovered in a watery grave.
Gardner also pleaded guilty to attempting to rape a jogger near the spot where he attacked Chelsea.
It's been six months since John Gardner attacked me. Sometimes I still wake up screaming," said Candice Moncayo, who survived the attack by Gardner.
Family members also criticized the legal system. Gardener was convicted of molesting and beating a 13-year-old girl in 2000. He could have served a maximum of 11 years in prison for the crime but was released after five years.