Bullets that hit a U.S. Border Patrol agent’s car in California Sunday morning may have been fired from across the border in Mexico, according to U.S. Customs and Border Protection.

“Mexican authorities were contacted as the shooting appeared to originate from the Mexican side of the border. Mexican authorities responded and initially took two subjects into custody, one of them was in possession of a handgun, the other was released,” the CBP said in a Monday statement.