As the Mexican city of Monterrey struggles to recover from the effects of an arson attack on a casino which killed 52 people, corrupt local governance is again emerging as a major part of the story.

The clearest sign that the assault on the Casino Royale was linked to local government corruption, as well as to the broader decline in security in Monterrey, is the videotapes in which Manuel Jonas Larrazabal, the brother of mayor Fernando Larrazabal, is seen collecting huge sums of money from a local casino. This has led to speculation that he was involved in an extortion or money laundering scheme thought to have precipitated the attack, and he was detained by state authorities on Friday.

Mayor Larrazabal subsequently distanced himself from his brother’s activities and requested that the state investigate the videotapes. However, the national branch of Larrazabal’s PAN party has requested his resignation, a move the mayor has said he is considering.

Despite Mayor Larrazabal’s attempts to separate himself from his brother, and Manuel Jonas’s denials of any wrongdoing — he says he merely went to collect payment for some products that he sold the owner — the revelations have touched a nerve in Monterrey, which has suffered a dramatic decline in security since the beginning of 2010. One of the wealthiest cities in the country, and once one of the safest, Monterrey has seen its murder rate soar as Zetas and the Gulf Cartel fight for control of the region.

The potential links between government corruption and the Casino Royale massacre go beyond the mayor’s family. Investigations also resulted in the arrest of a state police officer, who is accused of having served as a lookout while the attackers set the casino ablaze. Nuevo Leon officials said that further arrests of police personnel were likely as the investigation continues.

Such collaboration between local police and criminal groups is not a recent phenomenon in Monterrey, though the rise in violence has increased concern about the issue. In diplomatic cable from March 2009, released by WikiLeaks, the U.S. consul general in the city warned Washington that half of the state and local police in Nuevo Leon were corrupt. Another WikiLeaks cable revealed that a former mayor of Monterrey and his counterpart in the wealthy suburb of San Pedro Garza Garcia were also suspected of receiving payments from casinos.

Largely because of this longstanding perception of local corruption, protesters were calling for Larrazabal’s resignation — as well as that of Governor Rodrigo Medina and President Felipe Calderon — in street demonstrations even before the news about his brother hit the airwaves.

If the nexus between authorities and criminals is nothing new, nor is the government’s response: purges of dirty officers. A spokesman for the Nuevo Leon government said that 100 state police officers would be removed from their posts by the end of the month, after failing to pass the vetting process. Of the 2,230 state police officers active when the current Nuevo Leon administration took office in 2009, only 1,090 remain in their posts, according to the spokesman, another demonstration of the aggressive purges that have been carried out.

Police purges — whether mass firings or mass arrests — are often publicized in the wake of allegations of police corruption. Just last week, authorities in the state of Hidalgo announced the arrest of more than a dozen police officers who were alleged to be working for the Zetas. Mass arrests and firings have been carried out among local police departments of cities like Veracruz, Torreon, and Juarez, among many others.

But one of the lessons of the Monterrey attack is that purging Mexico’s police forces is not something that can be effectively carried out overnight, nor as a one-off hastily carried out in response to a security problem. To be successful, it needs to be a continual process rather than a mere response to the suddenly emerging evidence of corruption. Yet efforts to build vetting into the Mexican security system have failed: according to government statistics from late 2010, just 22 percent of the nation’s police had been subjected to the vetting process that was initiated in 2008.

It also seems unlikely that an effective police purge will ever be possible in areas where the executive officials are themselves working with organized crime groups. For a local police officer, resisting the entreaties of organized crime in modern Mexico is a courageous decision regardless of the circumstances. But if the police’s political masters are themselves working with criminal groups, such a decision will seem futile: what can one police officer’s honesty accomplish when the entire local power structure is set up to serve organized crime? The answer is — very little.