Some notable incidents of mass violence Mexico's drug war over past year:

— May 13: Mutilated bodies of 49 people dumped on highway in northern Mexico.

— May 9: Dismembered bodies of 18 victims left near Mexico's second-largest city, Guadalajara.

— May 5: Bodies of 23 people found hanging from bridge or decapitated and dumped near city hall in border city of Nuevo Laredo.

— April 17: Mutilated bodies of 14 men left in minivan in downtown Nuevo Laredo, along with message from undisclosed drug gang.

— April 12: Tortured and bound bodies of seven men dumped in Pacific port city of Lazaro Cardenas along with messages signed by allies of Sinaloa drug cartel.

— March 18: Gunmen kill 12 police officers sent to Guerrero state to search for bodies of 10 people whose severed heads were found earlier.

— March 15: State lawmaker's body identified as one of 330 corpses found since April in mass graves in northern state of Durango.

— March 7: Sixteen bodies removed from three clandestine graves on outskirts of northern industrial city of Monterrey.

— Feb. 7: Suspected Zetas cartel member leads marines to mass graves at two ranches in Gulf coast state of Veracruz where at least 15 bodies unearthed.

— Nov. 24, 2011: Bound and gagged bodies of 26 young men found in vans and pickup truck left on expressway in heart of Guadalajara.

— Nov. 23: Seventeen burned bodies discovered in two pickup trucks in Sinaloa state capital, Culiacan.

— Oct. 6: Alleged members of New Generation gang allied with the Sinaloa cartel lead police to 32 bodies in city of Veracruz.

— Oct. 2: Seven bullet-riddled bodies dumped at bus stop in Pacific resort of Zihuatanejo, along with message from Knights Templar gang.

— Sept. 27: Five severed heads found in front of primary school in Acapulco.

— Sept. 20: New Generation cartel dumps 35 seminude, tortured bodies in front of terrified motorists at rush hour on busy avenue in Veracruz.

— Aug. 25: Two dozen gunmen burst into casino in Monterrey, douse it with gasoline and start fire that kills 53 people.

— July 26: Police find 18 bodies in clandestine grave near border city of Juarez in northern Mexico.

— July 8: At least 20 people killed when gunmen open fire at bar in Monterrey. Eleven bodies shot with high-powered rifles found earlier in day piled near well on outskirts of Mexico City.

— June 7: Federal officials announce finding 193 corpses in recent months buried in town of San Fernando in Tamaulipas state, most of them migrants kidnapped off buses and killed by Zetas.

— May 25: Twenty-nine people wearing fake military uniforms found heaped across roadway and inside bullet-riddled vehicles after battle between drug gangs in Pacific coast state of Nayarit.

— May 14-15: Officials blame Zetas for slaying of 27 workers at cattle ranch in northern Guatemala.