The city Medical Examiner’s Office said the cause of death of a 16-year-old Canadian boy who was aboard a tour helicopter that crashed into Pearl Harbor was brain trauma suffered while submerged.

Riley Dobson of Ontario died Feb. 22 at Pali Momi Medical Center, where he was taken after he was rescued from the cockpit of a Bell 206B JetRanger helicopter that crashed Feb. 18.

Rescuers said they had to cut his seat belt before they could free him from the helicopter in 40 feet of water, according to a preliminary report by the National Transportation Safety Board. Authorities initially said the helicopter was in 10-15 feet of water.

The official cause of death was anoxic encephalopathy, a condition that occurs when the brain is deprived of oxygen, the Medical Examiner’s Office said. The manner of death was accidental, the medical examiner said.

Also hospitalized at Pali Momi were Dobson’s parents. Another family member was treated at a hospital and released Feb. 18.

All of the family members returned to Canada after the couple was released from the hospital Friday, the family’s attorney said.

Pilot Ryan Rohner was flying the aircraft owned by tour company Genesis Helicopters when it crashed with four passengers aboard at about 10:30 a.m. Feb. 18 near the USS Arizona Memorial visitors center.

Rohner, who has been a UH-60 Black Hawk helicopter pilot with the Hawaii Army National Guard since 1999, was still hospitalized at Tripler Army Medical Center last week.

Rohner told a NTSB investigator that during a tour flight over Ford Island, he felt a vibration followed by a grinding noise. That was followed by a loud bang, and the pilot detected the revolutions of the engine rotor were slowing, the NTSB report said. The helicopter crashed after the pilot turned and attempted to land near the shoreline to avoid people near Contemplation Circle, the report said.