A 23-year-old inmate at the Two Rivers Correctional Institution died suddenly Sunday morning, becoming the fifth unanticipated death at the state prison this year.

Staff at the Umatilla facility were responding to complaints from Kenneth Allen when he became unresponsive, said Betty Bernt, an Oregon Department of Corrections spokeswoman. Emergency medical personnel arrived around 11 a.m., but were unable to save the young man — who had just three months remaining behind bars.

Allen, of White City, entered state custody in January 2016 on three counts of theft and one count of heroin possession in Jackson County, according to a Department of Corrections press release. His expected release date was Dec. 22.

Officials could not provide additional details or information at this time, Bernt said. The Oregon State Police Criminal Investigation Division will conduct an investigation, as is standard with state prisoner deaths deemed "unexpected" by the Corrections department.

Four other inmates at the prison, roughly 200 miles east of Portland, have died unexpectedly this year, according to press releases published on the Department of Corrections website. All of them were over the age of 50 and found unresponsive in their cells, the releases show.

Another six inmates this year have died at other Oregon state prisons, including Snake River Correctional Institution and Oregon State Penitentiary.

-- Shane Dixon Kavanaugh

skavanaugh@oregonian.com

503-294-7632 II @shanedkavanaugh