Updated

A report by a prosecution ballistics expert suggests that gunfire from a helicopter supporting Mexican Marines in a confused series of pre-dawn gun battles killed a female passerby and her two children.

Expert Anselmo Apodaca of the attorney general's office did not specifically blame the military helicopter for the civilians' deaths in the border city of Nuevo Laredo.

But he did say the bullets that hit the family's car came in through the vehicle's roof at a 45-degree angle.

Apodaca also said the car "was driving by chance in the line of fire of the shootout."

Photos of the scene showed a highway running through scrubby woods, with no apparent firing position offering a 45 degree angle down on the car's roof.