OKLAHOMA COUNTY, Oklahoma - An investigation is underway after an inmate died in custody.

Nicholas Green, 44, was booked into the Oklahoma County Jail after he was arrested by the Oklahoma City Police Department.

Police say Green caused a disturbance at a convenience store downtown. He was arrested for public drunkenness.

According to the sheriff’s office, Green was accepted into the jail at 8:45 p.m. on Monday. About 8:50 p.m., officers escorted him into a holding cell. At 8:55 p.m., Green appeared unresponsive and medical staff was notified.

After life-saving efforts, officials say he was transported to the hospital by EMSA where he was pronounced dead.

Green’s younger brother, Kenneth Green, is in shock.

He said, “It seems unreal. One second he is there and the next he is not.”

He said they were only two years apart. He is waiting for the autopsy to find out how his brother died.

“I never expected that he would die this soon, just out of the blue,” said Kenneth.

He said his brother may have had a drinking problem toward the end of his life, but thought he was trying to get cleaned up. Kenneth is holding onto the good memories of Nicholas Green.

“I looked up to him and I’m going to miss him.”