Armed assailants burst into a prison in the northern border town of Miguel Aleman on Tuesday and helped a dozen inmates escape, Mexican authorities said.

The incident occurred around 2:00 a.m. and two of the escapees were convicted murderers, the Tamaulipas state Attorney General’s Office said in a statement.

Fifteen armed men drove up in several vehicles and overpowered the guard at the access door, overcame the commander on duty, stole the keys to the cells and set the prisoners free, the AG’s office said.