(CBS) — Authorities have reopened the botched investigation into the 1991 rape and murder of a 14-year-old girl, which was wrongfully blamed on the so-called “Dixmoor 5,” some of whom spent two decades in prison.

WBBM Newsradio’s Steve Miller reports Cook County Sheriff’s investigators and Dixmoor police were re-examining the rape and murder of Cateresa Matthews, who disappeared after leaving her grandmother’s home in Dixmoor on Nov. 19, 1991. Her body was found a few weeks later in a field near Interstate 57. She had been killed by a single gunshot to the mouth.

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Sheriff Tom Dart called the case “horrific.”

Five teenagers, dubbed the “Dixmoor 5” were convicted of raping and killing Cateresa, but DNA evidence later cleared them. By then, James Harden, Jonathan Barr, and Robert Taylor had spent nearly two decades behind bars before they were cleared and released in 2011. Two others, Robert Lee Veal and Shainnie Sharp, served about 10 years in prison and were released before they were cleared.

Dart acknowledged DNA evidence already has linked another man to the crime, he said it’s too early to charge that man. Dart would not confirm speculation that the man is in prison already.

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“We don’t want to just take the easy, quick path and say, you know, ‘Let’s just mail this thing in. There’s been some DNA found. Let’s just go and do that,’” Dart said. “No, no, no. Let’s make sure we examine all the different nuances of this, because clearly this was a case that confounded people right when it happened, when usually things are a lot fresher. So, now, 20-some years later, why are we going to compound that by saying let’s rush to judgment on this.”

Dart said the investigation likely will take a couple months to complete.

“Clearly, I don’t think anybody would suggest there have not been mistakes made in the past on how this case was handled. Everyone understands that. We’re not going to go down that route. We’re going to be very methodical,” he said.

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Dixmoor Police Chief Ron Burge said he grew up with Cateresa’s mother, and for him, closing the case is personal.