A Wisconsin sheriff said Friday that his investigators had cracked a 20-year-old murder mystery.

Racine County Sheriff Christopher Schmaling announced that Linda Laroche, 64, of Cape Coral, Fla, had been arrested and charged with first-degree intentional homicide and hiding a corpse in the death of Peggy Lynn Johnson, 23, of McHenry, Ill.

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“We are very proud today by the fact that we can finally offer some closure and some peace,” Schmaling said, according to Fox 6 Milwaukee. "All of us here who have investigated the deaths of individuals during the course of our careers have seen many troubling things. However, the utter barbaric brutality inflicted on this young woman is something none of us will never forget."

In July 1999 a man walking a dog in Raymond, Wis., found the body of a young woman who had been brutally beaten and tortured. For two decades, the victim was known simply as "Jane Doe."

That changed in September, the Racine County Sheriff's Office received a tip that Laroche was “telling people that she had killed a woman back when she lived in Illinois.”

Mugshot, left, for Linda Laroche; Peggy Lynn Johnson (Lee County Sheriff's Office/National Center for Missing and Exploited Children)

The complaint states that investigators determined that in 1999 Johnson was a live-in nanny for Laroche’s children. It also says Johnson and Laroche met at a medical clinic where Laroche worked as a registered nurse several years before and that Johnson was cognitively impaired.

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The complaint says that investigators spoke to Laroche’s children who said their mother was very abusive to Johnson while she was living with them. One recalled her stabbing at Johnson's head with a pitchfork. La Roche's ex-husband confirmed the abuse and said the last time he saw Johnson, she was lifeless on the ground. La Roche told him that Johnson had overdosed and that she was going to take her from the house so the family wouldn't be involved.

When authorities first interviewed La Roche, she admitted that she abused Johnson, who moved in around 1994. She told different stories about how Johnson left the house, first saying she took Johnson to her grandmother, but later saying she drove Johnson to Wisconsin and left her at the side of the road. According to the complaint, she told authorities that Johnson wasn't injured and something must have happened after La Roche left.

The complaint says Laroche told investigators different stories about what happened to Johnson in 1999. It says that during a second interview LaRoche said she last saw Johnson when she drove her to Wisconsin and dropped her off.

An autopsy showed Johnson was malnourished, had been struck in the head shortly before death, and had a broken nose and broken ribs, some of which were broken after death and some that had been previously broken and were healing. She had also been burned, possibly with a chemical, over 25 percent of her body, and had branding marks on her body. The autopsy report shows she died from sepsis pneumonia due to infection from injuries she suffered during chronic abuse.

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Investigators exhumed Johnson’s body in 2013 with the hope of using advancing technology to identify her. She was reinterred in 2015, 16 years to the day that her body was discovered.

Laroche was arrested Tuesday and Schmaling said she had waived extradition to Wisconsin. Court and legal documents spelled the defendant's name variously as La Roche, LaRoche and Laroche, and it wasn't immediately clear which was correct.

Now that Johnson has been identified, authorities plan to exhume her remains again and rebury her next to her mother in Belvidere, Ill., Schmaling said. Her only surviving relative is a sister she never met.

The Associated Press contributed to this report.

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