I would prefer that the security guards were employed directly rather than contractors be used, for control and veting purposes more than anything.
To work at a British police station , either as an employee like a typist , cleaner or mechanic , you get vetted , if you enter as a contractor , a builder , decorator or caterer you still get vetted .
Though their home office did screw up recently with their cleaners didn't it .
It got security clearance for the actual company , but was doing the daily temporary security passes for the contractors employees due to a backlog in paperwork , when they finally got round to vetting the cleaners it turned out they were illegal immigrants