The FAA issued the directive at the request of St. Louis County Police and the stated reason was "TO PROVIDE A SAFE ENVIRONMENT FOR LAW ENFORCEMENT ACTIVITIES".
The police explained their request to the FAA by saying that a police helicopter had taken fire the night before.
The original Temporary Flight Restriction went into effect August 12 at 8:15am CDT and expires at 3:00pm CDT Monday 8/18.
The second order was requested by the office of Governor Jay Nixon. It went into effect at 3:00pm CDT 8/18 and lasts until 3:00pm CDT 8/25.