Gunmen opened fire on cattle ranchers, killing at least 11 in two weekend attacks in Mexico's southern Guerrero state, police said Sunday. Attackers traveling in 10 sport utility vehicles sprayed bullets at a ranch in the town of Petatlan before dawn on Sunday, killing five and wounding five others, local police chief Miguel Donatelo said. The property is owned by Rogaciano Alba, president of Guerrero's cattle ranchers' union and a former mayor of Petatlan, which sits 60 kilometers east of the Pacific resort town of Zihuatanejo. Six other ranchers were killed and five wounded on Saturday as they returned to their hotel from a union meeting led by Alba in the city of Iguala, Guerrero state investigators said in a news release. Police have not made any arrests or determined a motive for the attacks. Alba was investigated in 2002 for allegedly ordering the killing of Digna Ochoa, a human rights attorney who represented Zapatista guerrilla sympathizers and anti-logging activists in Guerrero.