RALEIGH, N.C. (AP) — Three U.S. Marines found unresponsive in a car at a North Carolina gas station died of carbon monoxide poisoning, the local sheriff’s office said Wednesday.

Deputies from the Pender County Sheriff’s Office found the three men Sunday morning in a privately owned car outside a Speedway gas station in Hampstead. Autopsies performed Wednesday by the North Carolina Office of Medical Examiner determined that all three deaths were the result of carbon monoxide poisoning, according to the sheriff’s office.

The Pender County Sheriff’s Office did not immediately make clear whether their deaths were accidental.

“I am saddened by the timeless and tragic death of these three young men, who served our country honorably,” Sheriff Alan Cutler said. “Our thoughts and prayers remain with their families and colleagues during this time.”

The lance corporals, identified by the U.S. Marine Corps as Tanner J. Kaltenberg, 19, of Madison, Wisconsin, Merax C. Dockery, 23, of Pottawatomie, Oklahoma, and Ivan R. Garcia, 23, of Naples, Florida, were stationed at nearby Camp Lejeune.