NORTH TEXAS (CBSDFW.COM/CNN) – For different reasons, they’d all been cleared for essential travel back to the United States — then three US Marines got on a flight in Japan, bound for Dallas/Fort Worth International Airport.

According to a Marine Corps. statement, Capt. Daniel Kult, Sgt. John Dietrick, and Pfc. Alexander Meinhardt were on the long-haul flight from Tokyo when a passenger barricaded himself inside a bathroom, began screaming and making threatening comments.

Dietrick said that even through the headphones he was wearing he could hear someone inside the bathroom who sounded “distraught.”

That’s when the Marines gathered outside the restroom while a flight attendant unlocked the door, according to the release. Once it was open, the leathernecks restrained the passenger with flex ties.

“I knew I had to step in when he became a danger to others and himself,” Meinhardt said. “I didn’t think twice about helping restrain him through the rest of the flight.”

After securing the passenger to a seat, the Camp Lejeune-based Marines who were about halfway through a six-month deployment in Okinawa, kept their eyes on the offending passenger for the remainder of the flight.

It’s unclear why the man, whose name has not been released, was distraught.

“At this time we cannot identify the airline or comment on the disposition of the passenger, as the incident remains under investigation,” said Marine spokeswoman 2nd Lt. Kayla Olsen.

The flight eventually arrived at DFW Airport after being diverted to Los Angeles International Airport so the passenger could be taken to a local hospital for a mental evaluation.

The US Attorney’s Office in California and the FBI are investigating the incident.

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