(PONTIAC) Authorities are investigating the suspected murder of a convicted killer by his cellmate at the downstate Pontiac Correctional Center early Tuesday.

Fabian Carrillo / photo from the Illinois Department of Corrections

Fabian Carrillo / photo from the Illinois Department of Corrections

Fabian Carrillo, 36, was found lying on the floor of his cell in the east segregation unit at the maximum security prison during a routine tour about 12:30 a.m. Tuesday, according to Illinois Department of Corrections spokesman Tom Shaer.

Carrillo was taken to St. James Hospital in Pontiac, where he was pronounced dead at 1:30 a.m., Shaer said. An autopsy was performed Tuesday, but authorities are waiting for the result of toxicology tests.

Authorities said Carrillo’s death is being investigated as a homicide. No sharp or blunt objects were found in the cell, and there was no sign of the use of those kinds of objects on the victim, Shaer said.

Carrillo’s cellmate was immediately arrested without incident, Shaer said. The two had been cellmates for more than two weeks and there were no reported incidents between them.

Carrillo was convicted of murder in Cook County and had been in prison since August 2003 serving a 52-year sentence, according to IDOC records.

The 33-year-old cellmate is serving a 22-year sentence for aggravated criminal sexual assault in Cook County, and had previously been convicted of aggravated robbery and narcotics charges, according to IDOC.

The DOC Investigations and Intelligence Unit and Illinois State Police are investigating. Shaer said charges will be pursued with the Livingston County state’s attorney after the investigation is complete.

“Any death is a sad even,” he said in the statement. “The Illinois Department of Corrections protects the safety and security of inmates and staff alike, and this department’s extremely low statistics support that statement.”

The homicide would be the fifth in the entire IDOC system in the last 5 1/2 years, and the first at Pontiac since October 1990, he said.

Illinois had 9 prison killings in the period from 2001-11, while in comparison, California had 142, Texas 38, and New York 17, he said

The prison remains on Level 4 lockdown, but visiting privileges have not been interrupted, Shaer said.