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WEIMAR, GERMANY - JUNE 04: A barbed wire fence stands on the grounds of the former Buchenwald concentration camp on June 4, 2009 near Weimar, Germany. U.S. President Barack Obama is scheduled to visit the site tomorrow. Obama's great-uncle, Charles Payne, was among U.S. soldiers who liberated the nearby subcamp of Ohrdruf in 1945. Thousands of Jews and other inmates died under horrendous conditions at the Buchenwald camp during World War II. (Photo by Sean Gallup/Getty Images)
The 37-year-old inmate was pronounced dead at the scene about 5 p.m. Monday, nearly seven hours after the incident began, the Illinois Department of Corrections said. His name hasn't been released.
The hostage, a 62-year-old female employee, was rescued and was being evaluated by medical personnel.
The agency says around 2,200 male inmates in the prison remain on lockdown and the facility is secure.
Corrections officials say the offender was serving a sentence for aggravated criminal sexual assault and aggravated kidnapping. The crimes took place in Cook County.