CHICAGO (CBS) — An inmate who was found unresponsive on a transport bus to Stateville Correctional Center last month died of a drug overdose, the coroner’s office announced Wednesday.

Clifford V. Nelson, 49, was being transferred from the Cook County Jail and was found unresponsive on the bus about 9:50 a.m. Feb. 27 at Stateville in Crest Hill, according to the Will County coroner’s office.

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Autopsy and toxicological reports revealed Nelson died from heroin, fentanyl and fentanyl analog overdose, the coroner’s office said. His death was classified as an accident.

At the time, Nelson was being transferred to Illinois Department of Corrections custody from the Cook County Jail on a parole violation, according to IDOC spokeswoman Nicole Wilson.

When the bus arrived, Cook County staff informed IDOC staff that Nelson was unresponsive on the bus, Wilson said. He remained in the custody of the sheriff’s office.

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He was taken to Saint Joseph Medical Center in Joliet, where he was pronounced dead at 10:53 a.m. that day, the coroner’s office said. There were no signs of foul play.

“He had come into our custody about a day-and-a-half earlier and there was no indication of distress or ingestion of any drugs at that time,” Cook County sheriff’s spokeswoman Cara Smith said. “His death is unfortunate and the Illinois State Police are handling the investigation.”

In April 2016, Nelson was sentenced by Cook County Judge Ramon Ocasio III to 18 months in prison for a charge of retail theft, court records show. He lived in Chicago’s Ashburn neighborhood on the Southwest Side.

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