An inmate of the Jefferson County jail died after she was found unresponsive in her cell.

At about 4:15 a.m. Wednesday, a Jefferson County Sheriff’s Office deputy was conducting routine cell checks when Jolene Dorothea Mathiesen, 45, was found unresponsive in her bunk, according to a news release. Life-saving efforts began, including CPR and the administering of Narcan, a drug that can reverse an opioid overdose.

Golden Fire and EMS arrived and continued life-saving efforts, which were ultimately unsuccessful as Mathiesen was pronounced dead at 4:56 a.m.

Mathiesen had been in custody since Monday and faced charges of a probation violation related to child abuse charges, the sheriff’s office said. The charges originated in Lakewood.

A cause of death was not available Thursday. The First Judicial District’s Critical Incident Team is investigating the incident. The Jefferson County Coroner’s office will determine the cause of death.