From Calderon's inauguration in December 2006 to the end of October 2012, 623,213 people were detained by Mexico's federal forces as part of their fight against organized crime, the Attorney General's Office (PGR) told Excelsior.

The majority of those arrested, 498,570, were freed, either because of a lack of evidence or because they were let out on bail.

The Attorney General's Office only managed to establish that 5,608 of the suspects were part of organized criminal groups.

InSight Crime Analysis

As Excelsior points out, the figures are inconsistent with those provided by other government institutions such as the Defense Department (Sedena), which reported that over 50,000 people linked to criminal groups had been captured in that period.

The statistic of 80 percent freed is an illustration of the high impunity rates in Mexico, but can also indicate an overeagerness by law enforcement official to capture suspects without enough solid evidence. In September, a report from the Attorney General's Office said that of some 3,439 people arrested on drug trafficking charges between 2006 and 2011, only 31 percent were convicted.

The figures also highlight the fact that even when the military and federal police are sent to combat drug trafficking organizations, as they were under Calderon's presidency, their power to carry out operations and detain suspects means little in the absence of an effective justice system to make sure that those captured go to trial. As InSight Crime has pointed out, a cycle of arresting and then releasing members of gangs could even be worse than not arresting them in the first place, as these individuals are held together for short periods of time in poor facilities, creating "universities of crime" where they form connections with one another.

New President Enrique Peña Nieto, who took office on December first, has promised to push ahead with reforms to the judicial system begun under Calderon.