CONCORD, Calif. -- Investigators with the National Transportation Safety Board are still searching for what caused a plane crash in Concord that killed four people.

Authorities say the pilot and two women died at the scene Thursday when the plane crashed onto a highway. The fourth victim, a 12-year-old boy, died during surgery at John Muir Medical Center in Walnut Creek.

The pilot has been identified as 78-year-old John Mauricio. Also killed in the crash was his wife, 73-year-old Alice, their daughter Alyce Mauricio Dreher and her son Robert.

The elderly couple is from Nevada. The daughter and her son are from San Diego.

The plane crashed about 11 a-m yesterday about 200 yards from the runway of Concord's Buchanan Field Airport.