DUBLIN, Calif. (KRON) — An inmate’s death is being investigated after a 39-year-old man died inside Santa Rita Jail in Dublin.

According to the Alameda County Sheriff’s Office, inmate Stephen Lofton was alone when he died inside his cell Tuesday night.

Lofton had been arrested by Hayward Police Department officers four days earlier for allegedly possessing a stolen vehicle and drugs.

On January 17 at 8:03 p.m., “Mr. Lofton was found unresponsive in his cell by deputies,” Alameda County Sheriff’s Lt. Tya Modeste wrote.

A jail-issued bed sheet was found around his neck and tied to the cell’s top bunk bed, according to Modeste. He was pronounced deceased minutes later by firefighter paramedics.

“The investigation is ongoing, but preliminary review of Mr. Lofton’s intake process and prior custodial history did not reflect any information that indicated he was potentially suicidal,” Modeste wrote.

Lofton’s father said his son had no known mental health issues, however, he suffered from “severe substance abuse issues,” according to the Sheriff’s Office.

The District Attorney’s Office was notified and an investigation report will be submitted to the California Attorney General’s Office.