@KyJane You are right. They wouldn't need to leave and would be notified by their superiors before anything like that took place. Otherwise it would be highly suspicious and they would have checked before leaving, since their asses would be on the line. Also, they don't do maintenance at night. This story, which appears to come from a single source (BNL News) who claims he won't reveal his source but has done so anyway (the two guards), is intended for ignorant people who don't know how things are done or just don't think.