But investigators didn't think the house showed signs of forced entry, and, more importantly, they figured it would take a great deal of planning or luck for the killer to sneak into the house and snatch Riley during the few hours when her father was asleep and her mother wasn't home.
They also wondered why Kevin waited 40 minutes after realizing his daughter was missing before calling the police. Kevin said when he was growing up he learned that the only time to call 911 is, "if there is a fire ... I never ... I never thought my daughter was kidnapped. Never, never in a thousand years," he said.
While they spent time canvassing the neighborhood and interviewing local sex offenders, the Will County Sheriff's detectives grew more interested in Kevin, the last known adult to see Riley alive.
They shot surveillance footage of him at Riley's funeral, and they took special interest in a security video from a gas station located between the Fox home and the creek where she was found. Investigators believed it showed a car similar to Kevin Fox's Ford Escape passing the station around the time of the murder.
The summer progressed with no named suspects, and public support for the family waned after a TV report portrayed the parents as indifferent to the death of their little girl. Rumors started swirling.
The Foxes sensed the community was turning, but Melissa never questioned her husband's involvement.
"I know Kevin way too well and watched him be a parent to our children every day," she said.
There was another dynamic at play. As the State's Attorney Jeff Tomczak was dealing with pressure to solve the case, he was also fighting for his political life, with Election Day was approaching.
A week before the election, Will County detectives called the Foxes and asked them to come to the station. After arriving, they were immediately separated.
Kevin was taken into a very small room and interrogated for the next 14 hours. According to Kevin's account, detectives told him they had reason to believe that he had killed Riley.
"They broke me down mentally, physically, emotionally… but I stayed strong. I knew… I, I denied everything, everything that they would say to me," he said.
Kevin said the investigators told him to take a polygraph test, and he agreed, confident he'd pass. But afterwards, detectives told him he had failed. Finally, Kevin broke, offering a statement admitting he killed Riley.
According to the investigators, Kevin said he woke up in the middle of the night went to the bathroom, where he accidentally hit Riley with the door, causing her to stumble and hit her head on the bathtub. Thinking he'd accidentally killed her, he panicked and supposedly did something to make it look like she was sexually assaulted. Investigators said he put duct tape over Riley's mouth, drove her in his car to the river and walked down the side of a small bridge and dumped her into the river.
Hours after making that statement, Kevin Fox was charged with first degree murder.
The next day, Tomczak announced he would be seeking the death penalty. "The young child in this case died a terrible death," Tomczak announced at the time, "And for that reason, the penalty deserves to be death."