Homicides were at historic lows in 2006 probably due to the fact that very few were confronting the criminals. I mean, if they can operate with impunity then there is less need for violence.
Violence also spikes whenever an upper level drug lord is taken down because there is a power struggle between rivals gang members as they fight to take his place. This is true whether it is the police or the military doing the law enforcement duties.
I do agree though that the police need to buck up, the military shouldn’t have to be running the show.