But McGonigle admitted on "The Early Show" it could just be that she's in denial.
McGonigle pointed to a possible link between Gardner wearing a monitor until 2008, and her daughter's disappearance a year later on February 13, 2009. Dubois was last seen at Escondido High School, in Escondido, Calif. Gardner lived just six minutes from her school and not far from where King disappeared.
She said, "I would think he would have been one of the very first people Escondido police department looked at."
"Early Show" co-anchor Harry Smith noted the widespread search for Dubois did include a focus on Gardner. Smith said volunteers monitored the registered sex offender and even took pictures of him.
"I don't know about the pictures," McGonigle said, "but I know he was one of them that our volunteers did monitor."
Following her daughter's disappearance, McGonigle said, the police performed their routine checks on all the sex offenders in the area where Dubois went missing -- including Gardner. However, she said she doesn't know if he was actually questioned by police.
McGonigle said she's looking for an end to their search "one way or another."
"Her dad and I both need closure," McGonigle said. "So -- not that we want to bury our daughter, but we need some closure."
When pressed why she didn't think Gardner had involvement with her daughter's case, McGonigle said she thinks it was another sex offender because Gardner "seems a little sloppy in what he does."
McGonigle said searches for Amber Dubois will resume on March 13.