(CNN) -- Carrie McGonigle doesn't want to believe that her missing daughter could be connected to a registered sex offender accused of killing a California teen.
"That would mean that she's dead, and I don't want to think that," said McGonigle, whose 14-year-old daughter, Amber DuBois, was last seen walking alone to school on February 13, 2009.
But authorities say they are looking into whether John Albert Gardner III, who pleaded not guilty Wednesday to raping and murdering Chelsea King, was involved in Amber's disappearance.
"We have been working closely with San Diego Sheriff's Office, and our investigators are working with theirs in case there is a connection," Lt. Robert Benton with the Escondido, California, Police Department said. "We are involved in the daily briefings on the King investigation."
Amber's father, Moe DuBois, attended Gardner's arraignment Wednesday.
"Just the similarities in our case, you know, if there is any connection to Mr. Gardner and our case, I want to be there for his prosecution and soon to be execution I would hope," DuBois told HLN's Nancy Grace.
Amber's family lives in the San Diego, California, suburb of Escondido, less than 10 miles from Poway High School, where King was last seen alive.
The shy, bookish teen was walking to Escondido High when she disappeared. She had a check in her backpack to buy a lamb for a Future Farmers of America project, according to her mother. But she never made it, and since then, investigators have been stymied by a lack of viable leads.
McGonigle says Gardner came up on her radar shortly after Amber disappeared, when she began looking up registered sex offenders in the area.
"One of the first things we did when we couldn't find her was look at the sex offenders in the area because we know that they have a history of repeated offenses," McGonigle said. "I didn't personally visit his home but one of our volunteers did, and we didn't find anything that raised suspicions."
Gardner is on California's sex offender registry for a conviction of lewd or lascivious acts with a child under 14, according to online records. He was also charged Wednesday with assault with intent to commit rape in connection with an attack on a jogger in December 2009.
A call to Gardner's public defender, Michael Popkins, was not immediately returned.
In addition to keeping the search going for her daughter, McGonigle has also become involved in educating parents and children on how to prevent abductions. She also spends time reaching out to parents of other missing children.
As soon as she learned of Chelsea's disappearance, McGonigle says she contacted Chelsea's parents and assisted in search efforts. Chelsea's car, with her cell phone inside, was found at the Rancho Bernardo Community Park, where she was known to go for runs.
"Ever since Amber went missing I've reached out to all the parents I possibly can because once it happens to you, it's going to be with you the rest of your life," she said. "It becomes your life. Supporting families, that's what it's all about. Even when we find Amber, I'll continue because I wouldn't want any other family to go through this."
Searchers found a body Tuesday that they believe to be King's, San Diego County Sheriff William Gore said at a news conference Tuesday. He said he expected a positive identification of the body to come this week.
To some in Amber's family, Chelsea's disappearance has other stinging implications.
"It's heartbreaking in another way because now we know of everything that was available to search for Amber but wasn't used," Sheila Welch said. "There weren't helicopters used with heat sensitivities, there weren't any dogs brought out for Amber, and now to know that's available, it's heartbreaking to think it wasn't used."
But Benton said investigators used all the resources available to them.
"We asked for and received the resources we needed at the time," he said. "As far as law enforcement is concerned, we had outstanding cooperation from local agencies, the FBI, the National Center for Missing and Exploited Children, and we had a significant amount of resources at our disposal."
Amber's mother has her doubts as to whether Gardner could actually be involved.
"I think the guy is too sloppy and that we would've found some evidence if he had taken Amber," she said. "But he never should have been out in public. If he were incarcerated, like he should have been, maybe Chelsea would be alive right now."