Regarding the recently announced TFR for the Ferguson, MO area, what is the process by which such a TFR is granted?

The official reason given is "TO PROVIDE A SAFE ENVIRONMENT FOR LAW ENFORCEMENT ACTIVITIES", but the optics of the situation somewhat differ. Given the previous orders by local police for media to leave the area and the 3000ft ceiling of the airspace, there has been significant commentary on social media arguing that this may be a politically-motivated act to prevent the media from scrutinizing the actions of law enforcement (for instance here).

As far as I know, there is no (public) information regarding threats to airborne vehicles, and despite some initial reports most of the protests in the area have been peaceful. I'd like to assume we're still living in a free and fair country, and that this TFR was created for legitimate, non-political reasons.

Is it common for the FAA to grant a TFR like this to local police? What is the process by which this is done? What criteria are considered by the FAA in determining whether such a TFR is warranted?