There is always a wave of murders when the drug franchise issued from the Mexican power structure changes. The new boss is simply eliminating his competition, probably with the assistance of Federal police.
i live here, and don't much worry about gangsters bumping each other off. Unlike the gangs in the U.S., folks here normally don't take out innocent bystanders. But, the feeling in Mexico is that the problem is caused by the U.S. (yeah, I know... Mexicans blame EVERYTHING on the U.S. -- and some folks here blame everything on Mexicans so it's a fair trade). There's more than some truth to the matter. Drugs are one export the U.S. isn't trying to regulate off the market (unlike fruits and vegetables, but that's another thread)... the U.S. is the world's largest consumer of these products (50% of the world's narcotics are consumed in the U.S., according to the CIA's world fact book).
The Mexican response is to blame the violence on the U.S. drug consumers. Hey, most here want capitalism... this is just the ugly side of it.