What FARs cover R/C drones?

The following news item has the FAA on the Los Angeles' sheriff's case
about the sheriff's use of R/C planes. I've searched the FARs in the past
to see if I could find what regs covered radio controlled (or more
interestingly, autonomous) aircraft and came up with nothing. I think the
Sheriff has a valid question in asking why they need a "certificate of
authorization" but Joe citizen does not. Here's a link to the story and
relevant quoted portions:

http://www.mercurynews.com/mld/mercu...a/14875403.htm

"Federal authorities have temporarily grounded Sheriff Lee Baca's plans to
fight crime using unmanned surveillance drones.

Baca hopes to use the small, remote-controlled planes to monitor events
such as standoffs and hostage situations, and search for fleeing suspects.
Last week, sheriff's officials demonstrated one of the 3-foot-long planes
in an abandoned field, showing it take off, beam video images 250 feet to
deputies below, and land.

The test, however, irked officials from the Federal Aviation
Administration, who said they had told the Sheriff's Department that it
needed a certificate of authorization from the FAA before flying the
planes."
....
""A private citizen can go to the store and buy one of those model
airplanes and fly them around. But because we're doing it as a public
service, we have to deal with the FAA?" said Sheriff's Cmdr. Sid Heal."

So what are FARs cover R/C aircraft (is there a weight or size threshold)?
Also, what FARs would cover autonomous (robot controlled) aircraft?