Unreported World investigates how Mexican crime gangs threaten, kidnap and kill news journalists

This week's Unreported World on Channel 4 investigates the growing number of journalists who are being killed, kidnapped or "disappeared" in Mexico as they try to report on drug violence and the growing links between the cartels and corrupt police and politicians.

Reporter Evan Williams and director Alex Nott travel to Ciudad Juarez, on the US border, to experience the daily life of a journalist who has been called one of the most courageous women in Mexico.

Luz Sosa is chief crime reporter on El Diario, the main newspaper in Ciudad Juarez, where more than 3,000 were murdered last year as powerful drug cartels fight for control of routes to smuggle cocaine and heroin into the US.

Two years ago, Luz's predecessor, crime reporter Armando Rodriguez, was shot dead in front of his home as he was about to take his children to school. Nearby in the office there is another small flower by the photograph of Luis Carlos Santiago, a 21-year-old photographer. In September 2010, Luz got a call that there was another murder. They arrived at the scene to find their colleague dead.

It was after she wrote up this story that she too received a direct threat. Her front-page article was found next to a severed human head on the outskirts of the city.

The Unreported World team also meets TV journalist Arturo Perez. He tells Williams that crime gangs, corrupt officials or police could be responsible for the killing and disappearances of journalists but there is never any credible investigation into these killings.

Across the border in the United States, Williams and Nott meet one of Juarez's leading journalists, who has been given asylum. He claims that after he published an investigation into corrupt officials linked to the cartels he received a threat from an official in the state governor's office that he would be the next journalist to die.

• Mexico: Living With Hitmen is broadcast tromorrow (Friday, May 20) on Channel 4 at 7.30pm
• Pic: Bullet casings collected by El Diairio crime reporter Luz Sosa to prove police are not collecting them for evidence. Channel 4
  
• Josh Halliday has interviewed Luz Sosa in the Guardian.