Three U.S. Marines who were found dead inside a parked car at a gas station in North Carolina on Sunday were determined to have died from carbon monoxide poisoning, Breitbart reported.

That determination came from the North Carolina Medical Examiner's Office on Wednesday, according to the Pender County Sheriff's Office.

The sheriff's office further noted that no drugs were found in the vehicle with the deceased Marines and there were no suspicions of foul play.

Deceased Marines identified

ABC News reported Wednesday that the U.S. Marine Corps had identified the three deceased individuals as Marine Corps Lance Cpls. Merax C. Dockery, 23, of Pottawatomie, Oklahoma; Ivan R. Garcia, 23, of Naples, Florida; Tanner J. Kaltenberg, 19, of Madison, Wisconsin.

All three men were stationed at Camp Lejeune, which is not far from the Speedway convenience store and gas station in Hampstead where the men were found Sunday morning during the course of a missing persons investigation.

"My deepest sympathy and condolences are extended to the family, friends, and colleagues of Lance Cpl. Kaltenberg, Lance Cpl. Dockery and Lance Cpl. Garcia," Brig. Gen. Michael E. McWilliams, the 2nd Marine Logistics Group's commanding officer, said in a statement. "Our focus is providing the necessary resources and support to those impacted by their tragic loss as they navigate this extremely difficult time."

Mother's phone call led searchers to missing Marine

In a Tuesday press release, Pender County Sheriff Alan Cutler said, "I am saddened by the timeless and tragic death of these three young men, who served our country honorably. Our thoughts and prayers remain with their families and colleagues during this time."

The release noted that sheriff's deputies were already conducting a separate missing persons investigation when they received a call Sunday morning about another missing person -- a Marine who failed to arrive on a flight home as expected and who was believed to be in the area of Hampstead where the missing Marine and two others were discovered at the convenience store.

According to USA Today, that call to the Sheriff's Office Sunday morning had come from the mother of Lance Cpl. Dockery, Heather Glass, who became concerned when her son didn't arrive home on a Saturday evening flight to Oklahoma City for his grandfather's funeral as expected.

She proceeded to make contact with Dockery's sergeant at Camp Lejeune as well as the Sheriff's Office and was able to direct both Marine and deputy searchers to the location where the bodies were found based on pings she sent to her son's cellphone.

With regard to the reported manner in which he had died, carbon monoxide poisoning, Glass told the media, "I feel at peace because I know he was asleep when he passed."

Investigation remains ongoing

USA Today reported that per the Marine Corps, all three of the deceased Marines were classified as "motor vehicle operators" and had been assigned to the 2nd Combat Logistics Battalion, 2nd Combat Logistics Regiment, of the 2nd Marine Logistics Group at Camp Lejeune.

Garcia was the longest-serving of the three, having gone on active duty in July 2019, followed by Dockery in June 2020 and Kaltenberg in May 2021.

According to ABC News, the Pender County Sheriff's Office is continuing to investigate the incident, and USA Today noted that spokesman Sgt. Chester Ward acknowledged that it remained unclear at this point how long the vehicle had been parked outside the gas station, if there had been any issues with that vehicle, or where the three Marines may have been going when they tragically died.