Who Watches the Watchmen?

The TSA, which spent $2 million of your tax dollars on equipment it has sitting unused in warehouses, is now outsourcing to private firms at 16 airports! Instead of government employees, our security is being outsourced to... whom exactly? Who are these private individuals (not government-screened employees) who are patting down passengers and rifling through their belongings, and how do we know they are not thieves, child molesters, or terrorists themselves? Unlike the government, these private firms are solely concerned with hiring cheap labor and maximizing profits. Who's watching the watchmen?