Ricardo Najera, a spokesman for Mexico's Interior Ministry said authorities allowed a group of inmates to leave the Cereso prison in Gomez Palacio, in Mexico's Durango state, in police vehicles to launch an attack on revelers at a farm in Torreon, in the neighboring state of Coahuila.

"The delinquents were committing their executions as part of a debt-settling scheme against members of rivaling groups from organized crime," Najera said Sunday of the July 18 attack.

"Unfortunately, in these executions, these delinquents also cowardly murdered innocent civilians," he said, adding that the inmates returned to the prison after the attack.

Four top Cereso Gomez Palacio prison workers, including the prison's director, were named as suspects in the investigation, Najera said.

The interior ministry said on July 25 that the four suspects had been "detained," but it was not clear whether charges had been filed.

Police were able to trace the weapons used in the July 18 incident to other violent attacks, Najera said.

Mexico's interior minister, Francisco Blake, said Sunday that the Gomez Palacio prison incident sheds light on Mexico's tenuous security and the "deteriorating state" of Mexico's local law enforcement.