"Chelsea's Law," signed by former California Governor Arnold Schwarzenegger, is designed to put child predators away for good.

Chelsea King, 17, was the quintessential all-American girl: An outgoing, compassionate, pretty, straight-A high school student. She went out for her daily afternoon run in her hometown of San Diego on Feb. 25, 2010. She never came home.

"I had just gotten home from the gym and Kelly had just gotten home from running errands at the grocery store and we met in the kitchen and she asked me if I had heard from Chelsea yet, because Chelsea's the kind of kid who always tells us where she is," said Brent King, Chelsea's father. "We just had this feeling. As parents do, I think."

Her disappearance rocks the community to its core.

"As much pain as Kelly and I and our family are in, the community is lifting us up and just embracing us, and without that we'd be really, really unbearable," said Brent King.

Crime Watch Daily affiliate KSWB was on the scene as law enforcement and thousands of volunteers ramp up the frantic search.

"The intensity of the search continued to increase throughout the weekend," said Brent King. "What we know about Chelsea is that she's a really bright kid and she would do everything she could to let us know where she's at."

Then, 72 two hours into the search, cops find a devastating piece of evidence: Chelsea's underwear is found near where she was running.

It contains DNA of John Albert Gardner, a convicted sex offender who served five years for lewd acts with a 13-year-old girl.

Cops arrest Gardner on suspicion of rape and murder.

Two days later, a dramatic announcement: "Although positive identification has not been made, there is strong likelihood that we have found Chelsea," said San Diego County Sheriff William Gore.

Then, the heart-wrenching confirmation: "The body was found not far from where we had previously discovered a piece of evidence, a shoe. It was about 15 feet away from a tributary that leads down to the lake, and it was covered in a shallow grave," said Gore.

But Gardner's reign of terror is not done. There is another horrifying revelation: Gardner has more victims.

While in custody, he leads police to the remains of Amber Dubois, a 14-year-old who had been missing for a little more than a year. Police say that she too was raped and murdered by Gardner.

In a chilling prison interview with author Caitlin Rother for her book Lost Girls, Gardner describes Amber Dubois's murder, telling Rother, "the picture of stabbing her is not a memory I'd like. I thought I'd like it, but I didn't. I like the raping part. I don't like the killing part, especially if it's bloody."

"The defendant in this case was just arraigned on two counts. The first count is murder. Attached to that count is the special allegation that the murder was committed during the commission or attempted commission of a rape," said San Diego Deputy District Attorney Kristen Spieler.

Gardner pleaded guilty to the murder and rape of both Amber Dubois and Chelsea King. He's serving two terms of life imprisonment with no possibility of parole and a third life term for a separate case of assault and attempted rape.

Could these twin tragedies have been prevented? In his probation report stemming from his prior conviction, a court-appointed psychiatrist called him "a danger to the community."

"He is simply a bad guy who is inordinately interested in young girls," the report says.

Out of the tragic darkness, the King family brings a ray of light. They champion a law that bears their daughter's name. "Chelsea's Law" is signed by then-Governor of California Arnold Schwarzenegger. It's designed to put child predators away for good.

"When we passed the law we said we wanted a law that targeted the worst of the worst, that you can't rehabilitate, you can't reoffend," said former California Assemblyman Nathan Fletcher (R-San Diego). "So we wanted that one-strike life without the possibility of parole to make sure the John Gardners of the world who did it the first time would never get out again to do it a second time."

"I have nightmares every night," said Tyler King, Chelsea's younger brother. "I have pretty bad ones. I don't really want to talk about them. They're pretty bad. They wake me up at night."

Tyler King was just 13 when his big sister's life was brutally ripped away. The events of those days are seared in his memory.

At 17, Tyler made the documentary "Chelsea's Light: A Brother's Journey," hoping that one-strike laws become the rule of the land against the worst child predators.

"Our son has not only survived this but he's thrived through it," said Kelly King, Chelsea's and Tyler's mother.

The Kings have also established the Chelsea's Light Foundation, dedicated to protecting kids and working to have Chelsea's Law passed in states beyond California.

The law might have saved countless girls. More than 1,000 predators have been charged under the California law that bears her name. And though it came too late to save Chelsea, her light will burn forever in the hearts of her family.

Gardner now spends his days in Corcoran, Calif., in one of the most high-profile prisons in the state. Some of his fellow inmates include Charles Manson; Phillip Garrido, the man convicted of kidnapping and raping California girl Jaycee Dugard; and Mexican serial killer Juan Corona.