A U.S. Marine was killed early Monday morning in Southern California when he was struck by a box truck as he was aiding motorists on the side of the highway, authorities said.

The Marine had been helping a couple in an SUV who had been in a crash on Interstate 5 in Oceanside, about 55 miles (88.51 kilometers) north of San Diego, at about 3:30 a.m.

The SUV’s driver had lost control and crashed and the vehicle was left in the freeway’s traffic lanes with no lights on, according to multiple media reports. The Marine immediately went to help the SUV’s occupants.

A box truck, driven by a 47-year-old man, crashed into the SUV. The Marine died at the scene and the SUV’s occupants were taken to a hospital.

“He was trying to do the right thing, he was trying to help somebody in need,” according to a statement from the California Highway Patrol reported by CBS 8. “Unfortunately, the freeway traffic was still moving at the time and the box van came and collided into the vehicle.”

The serviceman, whose name has not been made public, was 20 years old and stationed at nearby Marine Corps Base Camp Pendleton, according to The San Diego Union-Tribune.

“Our deepest condolences are with the Marine’s family, friends and unit service members,” the base said in a statement reported by CBS 8.

California Highway Patrol Sgt. Nicole Pacheco told The San Diego Union-Tribune that the SUV’s driver would be booked into jail on suspicion of multiple felonies after treatment at the hospital.