A massacre at a drug and alcohol rehabilitation center in the city of Torreón has become the latest crime targeting recovering addicts in Mexico. Eleven people died on the scene when gunmen burst into a drug rehab center Tuesday and opened fire. Another two victims died hours later from their wounds.

This is at least the fifth massacre targeting a rehabilitation center since 2008. Police suggest they are the result of score-settling between criminals, but murders here are rarely investigated with rigor.

Tuesday’s attack occurred as authorities had supposedly increased security measures in the city ahead of today’s visit by a cross-country caravan led by poet Javier Sicilia. The caravan, which is protesting the militarized drug war, is making stops in some of the northern areas hardest hit by related violence.

The massacre also comes amid multiple discoveries of mass graves in the north. Dozens of pits containing burnt bones where discovered just south of the Coahuila/Texas border over the weekend. At least seven bodies have been unearthed this week in the town of Juárez, Nuevo León.

Meanwhile, Mexico’s Attorney General’s office has updated the number of bodies found in the 2 largest mass grave sites. To date, 193 bodies have been discovered in San Fernando, Tamaulipas and another 236 pulled from sites around the city of Durango. Most of the bodies remain unidentified.