(AP) -- The husband and wife who carried out the San Bernardino massacre had been radicalized and had taken part in target practice, once within days of the attack that killed 14 people, the FBI said Monday.

The details came out as thousands of San Bernardino County employees went back to work for the first time since Syed Farook, 28, and his wife, Tashfeen Malin, 29, launched their rampage five days earlier.

"We believe both were radicalized and had been for some time," said David Bowdich, assistant director of the FBI's Los Angeles office. But the said investigators are still trying to establish when, where and by whom they were influenced.

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. 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."

While there was no evidence the shooters were directed by a terror network overseas or were part of a broader plot, "the two of them had gone down the dark path of radicalization," he said.

Farook's estranged father, also named Syed Farook, told the Italian newspaper La Stampa that his son shared the ideology of the Islamic State group and was fixated on Israel.

Malik attended a religious school in the Pakistani city of Multan briefly between 2013 and 2014 but didn't receive a diploma, Farhat Hashmi, founder of Al-Huda International Seminary, said in a statement on her website. The school is a women-only madrassa with locations across Pakistan and in the U.S. and Canada.

Hashmi has been criticized for promoting a conservative strain of Islam, but the school has no known links to extremists. She said the organization was not political and denounced violence and acts of terrorism.

"It seems that she was unable to understand the beautiful message of the Quran," Hashmi's statement said, referring to Malik.

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Associated Press writers Rob Gillies in Toronto and Amy Taxin and Brian Skoloff in San Bernardino contributed to this report.