FRAMINGHAM, Mass. (AP) — A survivor of a crash that killed a 21-year-old man and his 25-year-old sister said she stayed alive for hours in the car submerged under water due to an air pocket in the back seat.

Brian and Jennifer Archila died Sunday after their vehicle flipped and crashed into a Framingham pond. Brian's girlfriend, 21-year-old Lilibeth Vasquez, told authorities her boyfriend ducked under the water inside the vehicle after the crash, trying to open the door to save the two women, but never came back.

Fire officials said the side airbags deployed and blocked the lock handle.

Framingham Fire Department Captain Mark Leporati said that when first responders got to the pond to remove the car around 7 a.m., they found only Vasquez alive following the overnight accident.

"There was no report of anyone being in the car, so we had no apparatus coming," Leporati said. "But as we approached, we could hear someone calling for help, and we knew it wasn't only a submerged vehicle."

Police have not disclosed what caused the accident, but they previously said the vehicle appeared to lose control after failing to navigate a left turn.

An investigation is ongoing.

Angel Chilin, a cousin of the Archila siblings, said Vasquez told the family the group was on their way home from a party in Hudson when the car went off the road and flipped into the pond.

"They did everything together," Chilin said of the siblings. "I guess it's fitting they died together."

Throughout the day, family members and friends visited the crash site to mourn and leave messages on a memorial poster.