In 2005, Torrance, CA, police officers searched the apartment of two men suspected of robbing a gas station.

There, the officers found a lengthy manifesto and a list of potential targets, including synagogues and military sites. They had stumbled on an Islamist terrorist cell in the advanced stages of an attack plan.

The San Bernardino massacre, which killed 14 people, has focused new attention on "lone wolf" terrorists who plan attacks away from traditional high-profile targets without directly coordinating with others, the Los Angeles Times reports.

While the FBI typically takes the lead in major terrorism investigations, local police officers and sheriff's deputies are the initial line of defense — especially in the case of home-grown plotters.