The FBI said Saturday it is helping Mexican authorities investigate the fatal shooting of two Arizona women in the Mexican state of Sonora.

The Attorney General’s Office of Sonora said both victims, ages 72 and 82, were found shot dead inside an overturned pickup truck Friday morning on the Sonoyta-Caborca highway.

Officials said an abandoned Ford F-150 pickup truck in the town of Quitovac was connected to the shooting after authorities discovered a stash of AK-47-style rifles, loads of ammo and ballistic vests inside the vehicle.

Sonora, a state in northwest Mexico that shares a border with Arizona, is a hotbed for drug cartel violence.

No motive for the slayings has been given. The FBI told CBS News that it is joining the investigation.

The State Department told CBS that one of the dead women was an American citizen and the other was a lawful permanent resident.

• Matt Delaney can be reached at mdelaney@washingtontimes.com.