Political violence from Mexico's drug cartels?

Last night someone threw some grenades into a plaza during Mexico's Independence celebrations in the capital city of Michoacán. The governor of Michoacán is claiming it was drug cartels. So far, 8 are dead and over 100 people are wounded, but the numbers or changing quickly. You can read more about it here or here (in English). If it does turn out to be related to organized crime, this would be the first time they have engaged in such an open attack on civilians, and during a symbolic political event. The consequences of this attack are likely to be pretty bad...

UPDATE 9/18/08: Just a quick update on these attacks. First, the number of dead is 7, not 8. There were a number of conflicting reports when I originally wrote the post. Second, it seems the attacks might be linked to the cartel, La Familia. I've read it might be related to different factions within the cartel that are fighting each other, or it may be a rival cartel that is striking at La Familia. La Familia has been attempting to spread its operations through Michoacán and Central Mexico, and may have pissed off some other cartel.