NEW YORK ( CNN ) -- One summer night in 2004 , 3-year-old Riley Fox lay asleep on a couch not far from her 6-year-old brother on a chair in the living room . Their father was sleeping in a nearby bedroom . The FBI joined the search for the killer of 3-year-old Riley Fox last month . Just before 8 a.m. , Kevin Fox was awakened by his son . The boy told his father that Riley was missing from the sofa . Fox searched for his daughter for 40 minutes inside and outside their Wilmington , Illinois , home and then called police , according to authorities . His wife , Melissa , was in Chicago participating in a charity walk , and when she found out , she rushed home . Nearly 500 volunteers , along with police and family , searched for the little girl . Her body was found later that day in a river in Forked Creek , Illinois , just 4 miles from the family 's home . She 'd been bound and gagged with duct tape , raped and drowned , according to the Will County Sheriff 's Office and the coroner 's report . It was June 6 , 2004 , the start of a horrific ordeal for the family . Fox was arrested and charged with the killing , only to be exonerated by DNA evidence . More than five years later , authorities have yet to capture Riley 's killer . Kathleen Zellner , Fox 's attorney , said that the crime scene was brutal and that the theory is that Riley was snatched from her home , sexually assaulted and then thrown from the bridge overlooking the river where she drowned . Because her hands were bound and her mouth covered with duct tape , she was unable to swim or save herself , Zellner said . According to Zellner , Fox says that the night his daughter disappeared , he had gone to a street fair while the children 's grandparents looked after them . On his way home , about midnight , Fox picked up his two sleepy children from their grandparents and put them to bed in the living room of the 500-square-foot cement box family home . Riley often fell asleep on the sofa and her 6-year-old brother on the chair near her while watching TV , Zellner said . Fox has said the front door was wide open when he awoke , Zellner said , as was the back door . He has said he locked the front door before he 'd gone to bed . The back door 's lock had been broken weeks ago ; they typically propped a stack of laundry baskets against it to keep it shut . According to the family , those baskets had been removed and placed on top of the laundry machine by someone other than family members . `` From the beginning , we believed that someone was already inside the house waiting when Kevin got home with the kids that night , `` Melissa Fox said . `` But it was clear that police were looking at Kevin suspiciously . '' Indeed , five months later , Will County sheriff 's officers arrested and charged Kevin Fox with the sexual assault and murder of his daughter . Zellner says the arrest came after authorities coerced a confession from him after 14 hours of relentless questioning . Fox spent eight months in jail , but DNA evidence from the rape kit conducted on Riley 's body finally exonerated him . There was no semen found during the autopsy , Zellner says , but saliva of an unidentified male was found on the duct tape covering Riley 's mouth and elsewhere on her body . In late 2007 , the family won a $ 15.5 million wrongful-arrest suit against the sheriff 's detectives . The Foxes believe that the perpetrator was someone in the community who had been watching and targeting their daughter for some time . `` For weeks before her disappearance , I could n't shake a feeling of uneasiness , strange noises at night outside our house , as if someone were lurking and watching us , '' Melissa Fox said . Zellner believes that another big clue was a red car similar to a Chevrolet Cavalier parked outside the Fox home that night , before Kevin Fox and his children returned home . `` It 's only been in the last few weeks that investigators have actively begun pursuing this case again , '' Zellner said , `` even though Kevin was cleared nearly four years ago . '' Last month , the FBI joined the investigation at the request of Will County State Attorney James Glasgow . FBI agents combed Riley 's neighborhood and talked with neighbors and other potential witnesses . `` The FBI is bringing unprecedented resources and expertise to this investigation , '' Glasgow said in a statement . `` We can not allow this horrific crime against an innocent child to remain unsolved . '' The family is offering a $ 100,000 reward , and the FBI is offering $ 10,000 for information leading to the arrest and conviction of the person or persons responsible for Riley Fox 's death . Anyone with more information is urged to call the FBI 's Chicago office at 312-421-6700 .
FBI joins investigation into death of 3-year - old Riley Fox , slain in 2004 . Riley was reported missing from school ; her body was found that day . Police initially suspected father in the killing , but DNA cleared him . Advocate for family criticized law enforcement for lack of progress on investigation .