Could a Former Neighbor & Convicted Sex Offender Be Connected to Disappearance of 11-Year-Old Mikelle Biggs?

Dee Blalock, a convicted sex offender and former neighbor of Mikelle Biggs has long been eyed in her 1999 disappearance near her home in Meza, Arizona

Mikelle Biggs had been missing only minutes when police and neighbors mobilized in the still-unsolved effort find her.

Mikelle, 11, was last seen outside with her younger sister, 9-year-old Kimber, on their suburban street in Mesa, Arizona, as evening approached on Jan. 2, 1999. But after Kimber briefly walked away and went inside, she returned and couldn’t find her sister anywhere.

The bike Mikelle had been riding lay dumped on the road, its wheel still spinning. Nearby on the ground were the quarters she’d been holding to meet the ice cream truck that she’d heard in the distance.

“Within an hour there had been fliers made,” Kimber, now 29, tells PEOPLE. “There were hundreds of people forming search parties.”

Alert to the possibility of a child predator, police right away compiled a list of all the registered sex offenders in the neighborhood and began to knock on doors.

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One of them, part-time landscaper and handyman Dee Blalock, lived across the street from where Mikelle took piano lessons, and a few doors from the home of Mikelle’s best friend.

During the small window of time that police believed Mikelle was abducted, Blalock had been watching a football game on TV in his garage, he told them. His wife backed him up. And when he let police inside his home, they found nothing.

“He was looked at that night, but he had an alibi,” says Jerry Gissel, a retired detective with Mesa police who worked on the case. “There wasn’t a whole lot we could do.”

The search continued elsewhere, as detailed in the latest episode of People Magazine Investigates, airing Monday night on Investigation Discovery. (An exclusive clip is above.)

A year later, however, the investigation returned to Balock with laser-focus after he was accused and convicted for a sexual assault and beating on a Biggs neighbor who told Mikelle’s mom, Tracy Biggs, that intuition led her to believe Blalock had abducted her daughter.

The Mesa, Arizona, street from which Mikelle Biggs went missing on Jan. 2, 1999. Mesa Police Department

Mikelle Biggs. Courtesy Biggs Family

Questioning Blalock’s alibi again, Gissel tells PEOPLE it started to crack.

Blalock’s wife “was really submissive to him,” says Gissel. With Blalock locked up, his wife revealed to police that she behaved as her husband dictated and that after she’d delivered sandwiches to him in their garage on the day Mikelle vanished, he’d told his wife to stay away and thus she couldn’t actually account for her husband’s whereabouts during the hour when Mikelle was taken.

Coupled with Blalock’s criminal past, which included three prior convictions for sexual assault, kidnapping and child molestation, that new uncertainty in his timeline suddenly made Blalock a prime suspect in Mikelle’s abduction and presumed murder, according to investigators.

Now serving 187 years in prison after the attack on the neighbor, Balock has never been charged in Mikelle’s case — although he allegedly made a jailhouse confession claiming his involvement, Mesa police Sgt. Kevin Baggs tells PEOPLE.

The investigation remains open.

“Everything in my eyes points in one direction, and that is Dee Blalock,” says Baggs. “But I think it’s equally important that we say it could be someone else. Until the killer, if it’s not him, comes forward and leads us to her body, we may never get those answers.”

(Earlier this year, a message hand-scrawled on a dollar bill found in Wisconsin which read “My name is Mikel [sic] Biggs kidnapped from Mesa AZ I’m Alive” brought brief hope before police ruled the message a hoax.)

Department of Corrections

Blalock “is a huge question in this whole thing,” says Gissel, “but he denies he had anything to do with it.”

That didn’t stop Mikelle’s parents, mom Tracy and dad Darien Biggs, from meeting with Blalock in prison to ask whether he did.

“Of course his reply was no,” says Tracy. “At one point he made the comment that he can’t be held responsible for what his other personality does. He claimed to have a split personality.”

“I just kind of thought, ‘Yeah, you’re crazy — you can too be held responsible,’ ” she says.

People Magazine Investigates: Gone in 90 Seconds airs Monday (10 p.m. ET) on Investigation Discovery.