Four vehicles, including an oil truck, collided on Middle Country Road, Route 25, in Ridge.
RAW VIDEO: Moments after crash, frantic 911 call
Police say a woman, her two adult children and a friend were inside in a Mazda that burst into flames after hitting the oil truck.
They have been identified as Jacquelyn McCoy, 55, of Calverton, her daughter, Mary Alice Booker, 36, of Riverhead, her son, Anthony McCoy, 33, and McCoy's friend, Tameka Foster, 42.
Photos: Fatal crash in Suffolk County
Police said Jamel Turner, 23, of Bellport, was driving a stolen 2018 Camaro eastbound on Route 25 when he crashed into the Mazda.
A passenger in the Camaro, 19-year-old Lonidell Skinner of Bellport, was ejected and killed.
Police say the investigation into the crash is continuing.
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