Two people from York County were arrested early Monday morning in Biddeford after a gun went off in the pickup truck they were traveling in, shattering the passenger window, Biddeford police said Tuesday.

A police officer first spotted the late-model red pickup truck traveling north on Route 1 at about 35 mph with its passenger door wide open, said Biddeford Deputy Chief Joanne Fisk.

Police stopped the truck near Elm and Drapeau streets. Inside were Justin Riggall, 35, of Kennebunk, and Jenna Ward, 30, of Arundel. The couple had been arguing, Fisk said.

Officers found shattered glass and a couple of shell casings inside the car, indicating that at some point the gun went off, Fisk said.

Riggall was charged with domestic violence reckless conduct, violating conditions of release and operating a vehicle with a suspended license. Ward was also charged with domestic violence reckless conduct.

Fisk did not specify who was believed to have fired the gun, which was found in the center console of the car. The incident is under investigation, Fisk said.

Both Riggall and Ward are scheduled to appear in Springvale District Court Wednesday afternoon.