Prosecutors in northern Mexico say prison guards armed inmates and temporarily released them so they could carry out drug-related murders. Witnesses say guards gave official vehicles and weapons to prisoners before temporarily releasing them from the prison in Gomez Palazio in the state of Durango. Witnesses say the prison killing squad sprayed at least 120 rounds of bullets at a party in nearby Torreon, killing 17 people on July 18. Attacks on February 1 and May 15 that killed a total of 16 people are now believed to have been carried out by the same prisoners. Northern Mexico has experienced an increase in murders in recent years as the Gulf cartel and Zetas gang fight for control of the drug trade.