An autopsy performed Friday showed that Ryan Brunn, a Dahlonega man who confessed to killing a 7-year-old girl in Canton, hanged himself with his sweatshirt in his Butts County prison cell.

The investigation by the Georgia Bureau of Investigation's Milledgeville Regional Office has not led to any clues that the 20-year-old died from anything other than suicide.

Brunn was being held in a single cell at the Georgia Diagnostic and Classification Prison in Jackson when he was found unresponsive around 4:15 p.m. Thursday, said Kristen Stancil, a spokeswoman for the state Department of Corrections.

By 5:37 p.m., Brunn was pronounced dead at a local hospital, Stancil said.

Brunn was sentenced Tuesday to serve life in prison without parole for the Dec. 2 killing of Jorelys Rivera.

He described in detail Tuesday how he carried out the crime at the Canton apartment complex where he had lived and worked as a maintenance man for about a month.

Before moving to Canton, Brunn lived in Dahlonega.

After his guilty plea, Brunn was transported to the prison in Jackson and placed alone in a cell for his safety, said Gwendolyn Hogan, also a spokeswoman for the Department of Corrections.

"He was interviewed by mental health staff on Wednesday and was not placed on suicide watch based on the counselors' findings," Hogan wrote in an email.

Rivera was reported missing after she left the complex's playground to retrieve sodas at her apartment for her friends.

Brunn described to the court how he lured the girl into a vacant apartment and sexually assaulted her. Afterward, he said he was afraid she would tell her parents so he "cut her."

When the girl didn't die right away, he beat and stabbed her, he said. Then he put her body in a blanket and dumped it in a trash compactor at the complex where it was found.

In court, Brunn apologized to the girl's family members who sobbed in the front row of the courtroom when he graphically described how he killed her.

Associated Press contributed to this report.