Ollie Gray was initially hired by Ramsey's parents, John and Patsy, in the 1996 case, but decades later says he continues to work on the still-unsolved murder for no pay.
"You have to look for something in order to find something," Gray said in an interview with the Today show, calling the local police agency "inexperienced" in dealing with such a serious case. "There are probably three or four people that should have been investigated earlier and still need to be investigated," Gray said.
The young beauty queen was found dead in her family's basement with duct tape over her mouth the day after Christmas. She, her parents and her then-9-year-old brother, Burke, were the only people in the home at the time.
Police launched an investigation into John, Patsy and Burke in connection with the murder but the trio were cleared of any involvement in the crime in 2008 – two years after Patsy died from ovarian cancer.
In 2006, accused sex offender John Mark Karr falsely confessed to the murder, but Gray told Today that a man named Michael Helgoth could be the real culprit.
"He was basically a hell-raiser," Gray said of Helgoth, who committed suicide in 1997.
Nearly 20 years have gone by and Ramsey's killer has yet to be found, but Gray said he has hope.
"Somebody out there knows what has gone on."
Boulder police told Today that two detectives are assigned to the case and receive and evaluate information regularly.