The captain of an oil tanker pleaded guilty to assault in state court Monday for fatally stabbing one of his crew members aboard the ship while it was docked in Honolulu Harbor.

Jong Geun Byun, 66, faces a maximum 10-year prison term at sentencing in October. He had been facing a mandatory life prison term for murder in the Jan. 12 stabbing death of 59-year-old Kim Jong Il. His guilty plea to first-degree assault is part of a plea deal with the prosecutor.

Byun was captain of the Hai Soon 39, a 3,878-ton petroleum oil tank ship registered in the Cook Islands and operated by a Singaporean management company. At the time of the stabbing, the management company was under federal investigation for dumping oily water overboard in American waters.

Kim was the ship’s chief engineer responsible for preventing oily water discharges.

Another crew member told police that Byun and Kim walked into his room arguing. Byun then kicked him out and locked the door. The crew member said he left and, when he returned, saw Kim on his back with blood on his chest, other crew members applying first aid and Byun still in the room. One of the other crew members told police he had seen Byun punching Kim.

A city ambulance transported Kim in critical condition to The Queen’s Medical Center where he died of a stab wound to his chest.

Federal prosecutors charged the Singaporean management company, Hai Soon Ship Management Pte Ltd., in April with failing to maintain accurate records and failing to report the oily water discharges. Company lawyers pleaded guilty on behalf of Hai Soon, which was sentenced last month to two years of probation and fined $1 million.