The slaying of 3-year-old Riley Fox was a crime that rocked the small community of Wilmington, Illinois.
The little girl was kidnapped from the living room of her own home in 2004 and was found face down in a creek in the Forsythe Woods, about two miles from the Fox residence. Riley had been sexually assaulted, bound, gagged with duct tape and drowned.
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It was not until six years later -- after police incorrectly charged the young girl's father, Kevin Fox, with the murder -- that investigators tracked down the man now they now believe to be the real killer.
Scott Eby, a 38-year-old imprisoned sex offender, was charged on five counts of first-degree murder and one count of predatory sexual assault last month, after DNA evidence allegedly linked him to the crime. He is expected to plead not guilty to the long-unsolved murder.
At the time of Riley's murder, Eby was on parole and living about a mile away from the Fox home. Eby had no connection to the Fox family, but he had an extensive criminal history.
Eby was sent to prison for a separate 2005 charge of criminal sexual assault of a family member, according to the Illinois sex offender registry. He has been in and out of prison since 1988 on charges including forgery and a string of burglaries.
The FBI got involved in the investigation in 2009, just months after "20/20" first reported on the case. Agents came to the neighborhood, conducted interviews and came up with new leads, according to Will County State's Attorney James Glasgow.
One of those leads came from Eby's former girlfriend, who lived down the block from the Foxes at the time of Riley's murder. During the months that she dated Eby, the girlfriend, who asked that her identity not be revealed, described him as a "dishonest" "creep" with a dark past.
"His mom told me when he was like 15 that, he was mad at his dad, and he cut his dad's brake lines," she said. "So that was creepy to me, and awful, and ... it was one of [the] many things that creeped me out about him."
She said she also found other parts of Eby's behavior disturbing, including one episode at a hotel where they got in fight and she said she saw a noose hanging there. She thought he would threaten suicide, but said the noose was later taken down.
More important to investigators, she recalled sitting with Eby in a memorial garden dedicated to Riley Fox where they discussed the girl's death.
"I was saying, 'I can't believe somebody did that to that sweet little girl.' And he said, 'Oh, that was such a shame, wasn't it?' And the way he said was like cold, like he didn't mean it," she said. "It was like an actor reading a script that didn't know how to act. And for some reason it just stuck in my head."
Eby's insincere tone struck her as odd and when the FBI knocked on her door by chance last year, she opened up to investigators.
"It was just an inkling I had that when they came I was very grateful to get it off my chest and tell someone what I felt," she said.
Eby had no connection to the Fox family, and his girlfriend doesn't recall him ever mentioning Riley's murder again, but his extensive criminal past was enough to land him on the FBI's list of potential suspects. Eventually, they tracked him down in prison.