Pima County sheriff's department.
Border Patrol agents and police found one body in the bed of the pickup truck and the other nearby in the desert. The identities of the victims have not been released.
Five other border crossers were found hiding in nearby brush and were turned over to Border Patrol after being questioned. The rest managed to escape into the desert on foot.
When asked if investigators suspect the attack was orchestrated by a militia, sheriff's department spokesperson Deputy Dawn Barkman said investigators are "looking into every possibility but nothing is conclusive."
The truck carrying the immigrants was traveling in a wash that is commonly used for "human smuggling," according to the sheriff's department. A wash is a river in the desert that is often without water.
This is not the first deadly attack by people reportedly dressed in paramilitary-style gear in the area. In 2007, four men armed with an assault weapon and wearing camouflage and berets ambushed a vehicle 40 miles north of Eloy and killed a smuggling suspect and wounded another person.
The attack comes as the Arizona legislature is considering a bill that would create a volunteer, state-sponsored and fully armed militia to aid the Border Patrol along the United States-Mexico border. Militia members would be able to pursue, arrest and detain individuals. The 300-person militia would cost taxpayers $1.4 million annually and would be under the control of the governor.
Rep. Raul Grijalva (D-Arizona) criticized the bill last month after an appropriations committee approved it.
"This legislation is not just silly and irresponsible, it's a public safety threat," Grijalva said. "To arm individuals, provide paper-thin weapons training and deliberately place them in danger disrespects the taxpayers of our great state and cheapens the professionalism of our border security agents."
Crossing the border can be a dangerous task beyond the threat of attack. Immigrants often die of dehydration or malnutrition while crossing the harsh Sonoran Desert and attempting to avoid arrest. The humanitarian aid group No More Deaths has documented 71 deaths of immigrants attempting the cross the Mexico-Arizona border area since October 2011.