The warden of the prison in the northern Mexican city of Torreon was gunned down while riding in a vehicle, a municipal police spokesman said.

Armed assailants attacked retired army Capt. Juan Manuel Lopez Matias, 45, late Tuesday afternoon while he was riding on the road linking Torreon with the nearby city of Matamoros, the spokesman told Efe.

Experts with the Coahuila state Attorney General's Office gathered 30 spent shell casings from AR-15 assault rifles and .45-caliber and 9 mm pistols at the crime scene.

A half hour before the attack, police officers found six plastic bags in that same city with several dismembered bodies inside, as well as a message that authorities refused to make public. Thus far, no further details have been provided about the grisly discovery.

Coahuila, which is on the border with the United States, has been the scene of a turf war pitting the Sinaloa and Gulf drug cartels against Los Zetas, a criminal organization that controls the state's largest cities, including Saltillo, the state capital, Torreon and Piedras Negras.

President Felipe Calderon declared war on Mexico's drug cartels shortly after taking office in December 2006.

Calderon has deployed tens of thousands of soldiers and Federal Police officers across the country to combat drug cartels and other criminal organizations.

Mexico's drug war death toll stood at 47,515 from December 2006 to Sept. 30, 2011.

The murder total has grown every year of Calderon's military offensive against the well-funded, heavily armed drug cartels.

Unofficial tallies published in December by independent daily La Jornada put the death toll from Mexico's drug war at more than 50,000.