An inmate found unconscious in his cell Sunday night at the Cumberland County Jail in Portland was later pronounced dead at the scene, according to the Cumberland County Sheriff’s Office.

An autopsy Monday on the body of Miles Hartford, 33, of Leeds was inconclusive and determining a cause of death will require further examination, according to a spokesman for the state Medical Examiner’s Office.

A corrections officer conducting a security check found Hartford at 9 p.m. Sunday. Corrections officers and medical staff performed CPR and summoned EMTs, according to a news release from the sheriff’s office.

Hartford is the first inmate in the custody of the Cumberland County Jail to die this year, said Sheriff Kevin Joyce.

The last inmate to die in jail custody was Karyn Victoria Kundishora-Nowlin, 30, of Portland, in July 2013, Joyce said.

Kundishora-Nowlin was taken to Maine Medical Center after a nurse working at the jail noticed her blood pressure was dangerously low. She was given CPR but died at the hospital, located just a few blocks away from the jail. At the time, she was being housed in the jail’s medical unit and was under observation for seizures.

The Portland Police Department, which investigates all deaths at the Cumberland County Jail, said there were no signs of injury or criminal activity in Kundishora-Nowlin’s death. Portland police are investigating Hartford’s death, and will be responsible for determining if it was suspicious, Joyce said.

The Cumberland County Jail was holding Hartford for the Androscoggin County Jail on charges including operating after suspension, violation of condition of release, operating under the influence and failure to submit to arrest. Joyce said that Hartford had been in the custody of the Androscoggin County Jail since August, and was only transferred to Portland on Wednesday.

Joyce said he was not sure why Hartford had been transferred, but said he heard second-hand that Hartford may have been facing charges in a Portland court.

Hartford was not on a suicide watch, Joyce said.

Steve McCausland, a spokesman for the Maine State Police, said state police investigate the cause of all inmate deaths in a state or county correctional facility with two exceptions – those that occur in Portland and Bangor. Last Friday, state police began an investigation into the death of an inmate at the Kennebec County Jail.