Who Killed Three-Year-Old Riley Fox?

After a young girl disappeared, her father became the prime suspect.

Nov. 5, 2008 -- Kevin Fox awoke on the morning of June 6, 2004, to some disturbing news. His son Tyler, 6, came into his bedroom to tell Fox that his 3-year-old daughter Riley was missing.

Fox was the only adult in the house. His wife, Melissa, had traveled 60 miles away, from their Wilmington, Ill., home to Chicago, to participate in a breast cancer walk.

Fox began looking around the house and in the yard, thinking perhaps his daughter was hiding or had gone next door to play with a friend. Instead, a horrific crime had occurred.

Later that afternoon, after dozens of volunteers in Wilmington turned out to search for the little girl, Riley's body was found in a nearby creek.

The Foxes always maintained that a stranger had come into the house and abducted Riley while Fox was asleep. As they grieved, the couple were comforted by tremendous support from the community -- attendance at Riley's wake and funeral was greater than the population of Wilmington.

But the police were suspicious; they didn't believe the house showed any signs of forced entry and what were the odds, they wondered, that an intruder would be able to get access to the house while Fox was asleep, on a rare night when his wife wasn't home?

Police were also suspicious of the fact that 40 minutes had elapsed between the time Fox said he learned Riley was missing and the moment he called police. Fox said he simply didn't consider the possibility that his daughter had been abducted and didn't realize it was an emergency until he'd done some searching around the house.

Police also took special interest in some security camera video from a gas station located between the Fox house and the creek where Riley's body was found. It appeared to show a vehicle similar to Fox's Ford Escape passing the station around the time of the murder.

The investigation was just the beginning of an ordeal that would see Fox arrested, jailed and charged with the murder of his daughter.

Did the young father kill his little girl? Or was he the victim of a full-blown frame job? To find out what happened, watch "20/20" Friday at 10 p.m. ET.