麻豆约拍

For the Mexican President, Felipe Calderon, there's clear evidence his war against the drug cartels can be won - and it's to be found in the border city of Tijuana.

Three years ago a tough, new police chief took over and joined forces with the military to aggressively attack the cartels. He also turned his sights on his own force, one of Mexico's most corrupt, and began purging officers suspected of working for the drug barons.

As a result, violence in the city centre has reduced. But there's a darker side to the war.

Dozens of suspects say have been tortured into making confessions. And in the poorer suburbs violence continues.

For Assignment, Rob Walker, investigates whether the war against the cartels is being won or lost in Tijuana.