Sex offender registries are designed to allow law enforcement and the public to keep track of those who may re-offend. But across the country, there are high-risk sex offenders who have not registered and authorities have no idea where they're living.
Matthew Lee Aiken is one of them. He was convicted of indecent assault and battery on a child, but failed to report his address. Police and the public had no idea where he was.
Inside Edition's Chief Investigative Correspondent Lisa Guerrero decided to track him down, documenting the process.
"Turns out he's very active on Facebook and his posts led us here to Worcester, Massachusetts, just outside Boston," Guerrero said while on Aiken's trail.
According to Facebook's policy, sex offenders aren't allowed to have profiles, but Aiken has been a member since 2008.
"We think he may be staying with a woman in the house across the street," she said.
The windows at the home in question were all blacked out.
"And check this out, there's a 'Caution Children' sign directly across the street," Guerrero pointed out.
Sure enough, there were plenty of kids playing right outside the home, which is actually a school bus stop.
It's problematic because as a level 3 sex offender, Aiken is considered high risk to re-offend.
Inside Edition's cameras captured Aiken leaving the home and going for a walk. He met up with a friend and together they hung out on a porch, smoking.
When he left, Guerrero approached him.
"Are you trying to hide the fact that you're a convicted sex offender?" she asked.
"No," he replied.
"Then why haven't you reported and registered your address with the authorities?" she countered.
"I've been busy," he answered.
"You've been busy, well we just saw you smoking," she said.
"Like I said," Aiken said. "I've been busy."
Aiken is not alone. Inside Edition found tens of thousands of other convicted sex offenders across the country that have apparently failed to register their addresses.
Laura Ahearn, director of Parents for Megan's Law, which tracks sex offenders, said it's a dangerous situation.
"Over 25% of the nation's registered sex offenders are likely not where they said they are going to be," she said. "And that makes our children and community members unsafe."
Asked whether people living nearby should be worried about him, Aiken insisted any concern was misplaced.
"Are your neighbors safe living near you?" Guerrero said.
"Of course," Aiken said.
Four days after Inside Edition reported him, police arrested Aiken at the same address and charged him with failing to register as a sex offender.
A Facebook spokesperson said: "We disabled [Aiken's] account per our Terms of Service."