Gunmen who killed 17 people at a party in northern Mexico earlier this month were let out of prison to carry out the attack, state prosecutors say

Guards at a prison in Durango state are accused of lending the inmates weapons and vehicles to commit the murders in neighbouring Coahuila state before returning them to their cells. The same group of prisoners are thought to have carried out other killings. The prison director and at least two other officers are under investigation. The killings in the city of Torreon in Coahuila state were traced to Gomez Palacios prison in neighbouring Durango state through bullets found at the crime scene, which matched assault rifles assigned to the guards, attorney-general's office spokesman Ricardo Najera said. "They were allowed out of prison to kill using the weapons of the guards and travelling in official vehicles" he said.