Corruption in the Mexican Police Force is a cause for the killings of police officers in the ongoing drug war that has killed 1,378 people this year. 

From the New York Times: 

The assassination was an inside job. The federal police commander kept his schedule secret and slept in a different place each night, yet the killer had the keys to the official’s apartment and was waiting for him when he arrived after midnight.

When the commander, Commissioner Édgar Millán Gómez, the acting chief of the federal police, died with eight bullets in his chest on May 8, it sent chills through a force that had increasingly found itself a target.

The police say the gunman had been hired by a disgruntled federal police officer who worked for a drug cartel in Sinaloa State, and the inside nature of the killing underscored just how difficult it is for President Felipe Calderón to keep his vow to clean up police corruption and end the drug-related violence racking Mexico.

Since coming to office in December 2006, Mr. Calderón has sought to revamp and professionalize the federal police force, using it, with the army, to mount huge interventions in cities and states once controlled by drug traffickers.

The result has been mayhem: a street war in which no target has been too big, no attack too brazen for the gangs.