Associated Press - June 19, 2009 5:44 AM ET

JOLIET, Ill. (AP) - The FBI has joined Will County authorities in their investigation of the 2004 murder of a 3-year-old Wilmington girl

Will County State's Attorney James Glasgow and FBI Special Agent-in-Charge Robert D. Grant announced the formal cooperation Thursday, and said FBI agents have been informally reviewing the case of Riley Fox for about a year.

Hikers found the girl's body in a creek four miles from her Wilmington home shortly after she disappeared in June 2004.

Her father, Kevin Fox, was later charged with first-degree murder and criminal sexual assault. He spent several months in jail before he was exonerated on DNA evidence.

A federal jury awarded Fox and his wife, Melissa, $15.5 million in damages after the couple accused Will Count sheriff's deputies of fabricating evidence.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.