HUNTSVILLE, Ala. (AP) - A fourth teenage girl died and four people remained in critical condition yesterday from a school bus crash in which the driver, who was severely injured, miraculously left the bus before it plunged about 30 feet off an interstate overpass.

Witnesses said a car struck the bus Monday morning on the I-565 overpass, causing it to swerve and plow into and over concrete railing, crashing nose-first into a street below.

One witness said the car hit the bus accidentally after possibly blowing a tire, while another said the car was speeding up and trying to get past the bus as lanes merged on the interstate ramp.

"He's real upset. He thinks it's his fault," said 17-year-old Chelsea Walker, who described herself as a friend of the car's driver. She said she had spoken to him Tuesday morning.

Authorities have not released the name of the driver in what police said is a criminal investigation. Police spokesman Wendell Johnson said evidence will be presented to a grand jury to decide if charges such as vehicular homicide or manslaughter are warranted.

He said a criminal investigation "does not mean a crime has been committed."

Police Chief Rex Reynolds identified the fourth victim of Monday's school bus wreck as Crystal Renee McCrary, 17. Like the other victims, she was a student at Lee High School in Huntsville who was on the bus when an orange Toyota Celica came up in a side lane, with the bus veering over the railing and crashing into Church Street below.