California shooters were radicalized for ''some time''

San Bernardino: Investigators believe the married couple who massacred 14 people in California last week - a US-born husband and his Pakistani wife - had been radicalized "for quite some time," but no clues pointing to an international plot have yet emerged, the FBI said on Monday.

Authorities also have evidence that Syed Rizwan Farook, 28, and his spouse Tashfeen Malik, 29, had engaged in firearms target practice near their Southern California home within days of last week`s deadly shooting rampage, according to the Federal Bureau of Investigation.

The latest disclosures in the FBI-led investigation came as San Bernardino County employees began returning to work under tighter security, five days after Farook, an environmental health inspector for the county, and Malik opened fire with assault-style rifles on a holiday gathering of his colleagues.

The couple died in a shootout with police several hours after their attack on Wednesday morning in a conference room at the Inland Regional Center social services agency in San Bernardino, about 60 miles (100 km) east of Los Angeles.

The FBI said last week that authorities are investigating the mass shooting as an "act of terrorism," noting that Malik, a Pakistani native who lived most of her life in Saudi Arabia, was believed to have pledged allegiance on Facebook to the leader of the militant group Islamic State.