MEXICO CITY, (Reuters) – A group of drug cartel  inmates who were allowed by guards to leave prison to commit  murders are believed responsible for the massacre of 17 people  earlier this month, the Mexican government said yesterday.

Mexico’s federal prosecutors’ office said in a televised  statement the prison staff, including the director, knowingly  let out the inmates at the detention center in Gomez Palacio in  Durango state.

“They were allowed to leave the prison and use the weapons  of the guards in these executions using official vehicles,”  said Ricardo Najera, the spokesman for the federal prosecutors’  office.

“These criminals carried out their executions as part of  the settling of accounts between rival gangs and disgracefully  these cowardly criminals then murdered innocent civilians on  their way back to their cells.”

Drug gang hitmen in five sports utility vehicles stormed a  birthday party in the northern city of Torreon on July 18 and  gunned down 17 revelers with automatic weapons. Another 18  people were wounded in the attack.

Two prison guards have so far been detained in the  investigation into the case, Najera said.

Torreon is one of the northern cities at the heart of the  struggle between rival drug gangs to control smuggling routes  into the United States.