In Mexico, drug cartels have become so powerful that they threaten to destabilize the state.
For two years, the president has waged a bloody war against them, especially in major cities near the U.S. border.
The fight remains unequal because drug lords have corrupted much of the municipal police.
Hidden cameras, surveillance and surprise inspections are used to track corrupt officers.
Those who dare oppose organized crime face threats of retaliation.
