The National Security Commission reports that the bus was carrying 29 unarmed officers dressed in civilian clothes Monday night to Mexico City, where they were to be on leave after 25 straight days on duty in the Pacific resort city of Acapulco.

The commission says the driver pulled over to check a mechanical problem near a toll booth in the state of Morelos. Armed men then boarded the bus, threatened him and the passengers and relieved them of their possessions.