In June, nearly 80 police officers suspected of working with drug smugglers were arrested in 18 towns.
Since then, Monterrey police have been banned from sitting in parked cars or using cell phones while on duty because of concerns they may be acting as lookouts for gangs. Police in Mexico’s third-largest city have also been prohibited from setting up sobriety checkpoints because they allegedly used them to extort motorists.

Earlier this year, the Cancun police chief was arrested on suspicion of involvement in the assassination of an army brigadier general hired to root out corruption in the city.

President Felipe Calderon has acknowledged that corruption permeates Mexican police at all levels. He has relied on the army to fight ruthless drug cartels, deploying tens of thousands of soldiers across the country since taking office in late 2006. Gang violence has since surged, claiming more than 13,500 lives.