Terrorists in Mexico

During the independence day festivities last night in Morelia, Michoacán, grenades exploded into the central square where the people were congregated. Seven people were killed, and dozens injured. 

This is an awful and puzzling crime. Mexico's leftist extremists (I mean the kind of people who think AMLO is a pawn of big business) are not known for attacking unarmed civilians, nor to my knowledge have they used grenades in the past. That would make you think of the cartels, and Michoacán's La Familia has suffered some setbacks at the hands of the government in recent weeks. Such a descent into terrorism would be unprecedented from a drug group, and, from the cartel's perspective, would seem to be a gigantic strategic error.