Seven alleged hitmen were shot dead by security forces in a separate incident in Morelos.

BBC: Mexico police chief killed as Morelos violence flares

He points to the incident involving Danny Fitzsimons - who shot dead Scottish security contractor Paul McGuigan and another colleague in Iraq in 2009 while suffering from PTSD - as evidence that the condition is a very real risk factor for those working as private security contractors.

BBC: Post-traumatic stress and the hired gun

The shooting left three security employees dead and a fourth critically injured.

CNN: Suspect in Canada killings caught at the border