CHICAGO (CBS) — The team that secured Juan Rivera’s exoneration in the Holly Staker murder case is now offering to help Waukegan Police find the girl’s real killer after 20 years.

Rob Warden, the executive director of Northwestern University’s Center on Wrongful Convictions, says there’s a good chance the 11-year-old girl’s killer can be found.

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Waukegan police have now reopened the murder case.

“It’s rather amazing to us that within about a mile radius of the murder scene in Waukegan–the home in which Holly Staker was murdered–there were more than 30 registered sex offenders,” Warden said.

Warden says his team has eliminated 10 of the 30 through DNA.

He thinks tests of the other 20 could prove helpful as investigators reopen the hunt for the killer. It was a murder that wrongfully sent Juan Rivera to prison for 19 years until he was freed on Friday.

An appeals court recently threw out Rivera’s third murder conviction for stabbing 11-year-old Staker in August 1992.

Rivera’s 2009 conviction was “unjustified and cannot stand” because of a lack of evidence tying him to Staker’s rape and murder, the 2nd District Appellate Court panel said in its 3-0 ruling in December.

Prosecutors then dropped the case against Rivera.