PEPPERELL —A 13-year-old boy who suffered life-threatening injuries after he was struck by a car while riding his bicycle on Sunday night is now in stable condition, authorities say.

The cause of the crash remains under investigation, Elizabeth Vlock, a spokesperson for the Middlesex District Attorney’s Office, said on Monday.

The boy was struck by a Chevrolet Malibu driven by a 62-year-old Pepperell man on Shawnee Road at about 7:15 p.m. Sunday, according to a press release issued shortly after the crash from John Guilfoil Public Relations, on behalf of the Pepperell Police Department. The driver of the car stayed at the scene of the crash and was cooperative with police.

The unidentified 13-year-old was wearing his helmet at the time of the crash, the release states.

The boy was transported by a Pepperell Fire Department ambulance to Nashoba Valley Medical Center in Ayer. He was then airlifted by medical helicopter to UMass Memorial Medical Center in Worcester.

Members of the Massachusetts State Police Collision Analysis and Reconstruction Section are assisting with the investigation.

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