Contralínea had a report earlier this week on the fact that of the 40,000 or so drug-related murders under Calderón, less than 2,000 have been picked up by the PGR. (I wrote about it here.) There appears to be a bit of a legal gray area; the PGR is obligated to pick up organized-crime related cases, but the agency says that murders are only on its list when the victims are federal employees or public servants. In any event, I think two other points are more relevant: one is that the issue would seem to be one of capacity more than the PGR laying down on the job. Notwithstanding the hundreds of employees who have been let go since Morales arrived at the top of the agency, pursuing 40,000 cases instead of 1,800 over a four-year period just wasn't possible with the PGR as it is presently composed.
That leads to the second point: given that the federal government wasn't able to investigate more than a few hundred murders a year, the states were necessarily going to have to be involved. Calderón couldn't have suspected that there would be 15,000 people dying per year, but well over a thousand people were killed in 2006 in drug-related crimes, and he should have suspected that his strategy would stir the pot and likely cause a spike in violence. As a result, prepping the state PGRs should have been a basic element of his strategy, but as far as I know, nothing like that happened in the ten days between his inauguration and the deployment of the army to Michoacán.