The Georgia Bureau of Investigations is looking into the death of a Georgia woman who died last week after falling out of a moving police car.

WMAZ reports Brianna Grier, 28, was pronounced dead on July 21 following an “in-custody incident with Hancock County Sheriff’s Office deputies.” The incident occurred on July 15, when Grier’s mother called police for help because her daughter was having a schizophrenic episode.

“Grier was arrested at the home,” the GBI said. “While deputies were taking Grier to the Hancock County Sheriff’s Office, Grier fell out of a patrol car and sustained significant injuries. She later died because of those injuries.”

According to Brianna’s father, his daughter suffered a head fracture and was airlifted to a local hospital. After remaining in a coma for several days, Brianna was taken off a ventilator after a doctor told relatives that she was “brain dead.”

Geoffrey Alpert, a professor of criminal justice at the University of South Carolina confirmed to NBC News that patrol cars are “ALWAYS supposed to be locked from the inside.”

“Otherwise,” he added, “prisoners would be letting themselves out all the time.”

“If she got out the car, they had to let her out the car,” Brianna’s mother, Mary Grier, told WMAZ. “That’s my interpretation, because in a police car, you can’t open the door from the inside, it had to be the outside.”

According to a news release from the GBI, agents conducted interviews, reviewed body camera videos and performed mechanical tests on the car. Automotive experts and the Georgia State Patrol assisted in the test to determine if there were possible mechanical malfunctions.

The GBI said Grier was placed in the back of the car, handcuffed in the front with no seatbelt. The investigation revealed that after she was arrested, they tried to put her inside the back seat of the deputy’s car on the driver’s side.

One of the deputies walked around and opened the rear passenger side door. The deputy went back around to the driver’s side. Both deputies put Grier in the back seat and closed the rear driver’s side door.

The deputy thought he closed the rear passenger side door, and the deputies left the scene. They drove a short distance before Grier fell out of the moving car. Body camera footage reveals the deputies had no contact with Grier from the time she was placed in the car until he fell out of the car.

The GBI investigation remains active and ongoing.