He also said the Muslim couple had taken target practice at ranges within the Los Angeles metropolitan area, with one session held within days of the rampage.
In addition, authorities found 19 pipes in the couple's home in Redlands, California, that could be turned into bombs, Bowdich said.
The couple opened fire with assault rifles Wednesday on a holiday luncheon for Farook's colleagues from the San Bernardino health department, where he worked as a restaurant inspector. The husband and wife were killed hours later in a shootout with police.
The reopening of much of the government's offices signaled an effort to return to normal for a community in shock and mourning.
"To honor them, to express our gratitude for their unimaginable sacrifice, we have to fight to maintain that ordinary," County Supervisor Janice Rutherford said of the victims. "We can't be afraid of our lives, of our community, of our neighbors, of our co-workers."
The Board of Supervisors said all facilities have increased security, including armed sheriff's patrols, and officials were considering additional permanent safeguards. Counseling centers and a hotline were open, and managers were urged to look for signs of distress in their employees.
Following the attack, the county shut down all but essential services, with many of its 20,000 employees staying home, county spokeswoman Felisa Cardona said.
While most employees went back to work Monday, those at the Environmental Health Services division, where Farook and many of the victims worked, will be off at least one more week, she said.
President Barack Obama said in a prime-time address Sunday night that the attack was an "act of terrorism designed to kill innocent people."
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