Investigators are working to determine the cause of a crash between a fire truck and pickup that killed three people, including an infant boy.

The crash happened at a Phoenix intersection on Sunday morning.

Police say the pickup driver, 20-year-old Kenneth Collins, was pronounced dead at the scene. A woman in the car, 19-year-old Dariana Serrano, and Collins’ 3-month-old son, also named Kenneth, were both pronounced dead at a hospital.

They say the fire truck was responding to an emergency call at the time of the crash and had its lights and sirens on.

Investigators say Collins made a left turn in front of the oncoming fire engine.

Police say the three firefighters on board are recovering from their injuries.

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(AP)