CHICAGO (CBS) — A Cook County Sheriff’s correctional officer remains hospitalized with serious injuries, after an inmate attacked him and two other guards early Tuesday at the Cook County Jail.

Around 3:40 a.m., a jail guard was passing out breakfast on a tier of the Division IX maximum security facility, when he opened a cell to let one inmate go down to the lower level to get a drink of water, according to the sheriff’s office. When the inmate returned, he grabbed the officer by the neck, and dragged him into the cell, attacking him with a sock filled with bars of soap.

The guard was able to exit the cell, but the inmate got on top of him on the catwalk outside the cell, and choked him until he lost consciousness, according to the sheriff’s office.

The inmate then stole the guard’s keys, and gave them to his cellmate, who let another inmate out of his cell.

Two other guards later arrived on the tier, and one of them confronted the inmate who had initiated the attack, while the other tended to the unconscious officer, according to the sheriff’s office. The inmate punched the officer who confronted him, knocking him unconscious, and then knocked the other guard to the ground.

A short time later, a sergeant armed with a stun gun arrived, and ordered the three inmates back into their cells.

The first and third guards involved in the attack were treated and released. The second was taken to the hospital to be treated for serious injuries.

The 30-year-old inmate who attacked the guards has been in custody since July 2017 on attempted murder and aggravated battery charges in the shooting of a Chicago police officer, after an armed robbery on the South Side, according to the sheriff’s office.

The sheriff’s office said they will seek additional criminal charges against that inmate and his cellmate, but CBS 2 is not naming either inmate, as they have not yet been charged in the attack.