Andrews International was hired by the Will County Sheriff's Department to scrutinize why detectives wrongly pinned the 3-year-old's murder on her father.
The report finds investigators ignored or missed key evidence that could have led them earlier to the man now charged with the 2004 murder, Scott Eby.
Police had Eby's shoes and his DNA evidence, but it took the FBI's involvement to finally close the case last year.
Instead, Riley's father, Kevin Fox, was charged and later released. He spent eight months in jail before DNA evidence exonerated him.
The Chicago Tribune reports Tuesday that in its 45-page report, Andrews determined the management of the investigation was almost nonexistent and police missed opportunities from the beginning that could have led to the killer.
The Associated Press contributed to this report.