Homegrown Terrorism and 'Bunches of Guys'

The train bombings in Madrid and London exposed the threat of "homegrown terrorism." Now the focus of law enforcement has changed from disaffected lone wolves to what the FBI calls "BOG's" or "bunches of guys." The New York Police Department pinpoints small groups of "unremarkable people" it says can be transformed into willing killers. The NYPD report calls the process a "road map" of radicalization which creates both opportunities and problems for law enforcement. Can local law enforcement take preventive action against BOG's without violating constitutional liberties? Why do the cops need satellite surveillance?