The FBI said Monday that it believes both suspects in last week's attack in San Bernardino, Calif., were radicalized before carrying out the mass shooting.

"We have learned and believe that both subjects were radicalized and have been for quite some time," said David Bowdich, assistant director of the FBI's field office in Los Angeles.

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Bowdich added during a press conference in California that investigators had "some indications of timeline" for when the pair were radicalized, but declined to elaborate.

Authorities had previously acknowledged reports that Tashfeen Malik had posted allegiance to the Islamic State in Iraq and Syria (ISIS) on Facebook under an alias.

Officials had also said that Syed Rizwan Farook, the male suspect, had communicated by phone with at least one subject authorities were monitoring who could be tied to terrorism.

Police announced last week that investigators had recovered a dozen pipe-bomb-type devices, bomb-making tools and thousands of rounds of ammunition in the suspects' home.

The FBI on Monday updated the figure of pipe-bomb-type devices recovered, with Bowdich saying, "Ultimately, it appears there were 19 pipes in that house that we have removed."

Bowdich said "some were in a bag" and had to be individually unpacked, and that they were not all bombs, but had the potential to be made into them.

Both suspects had participated in target practice, including just days before the Dec. 2 shooting, Bowdich said.

The shooting stoked fears of international terrorism on the heels of the Paris attacks last month, fears President Obama sought to allay in an Oval Office speech Sunday night.

The FBI on Monday shed light on to the breadth of its terrorist investigation into the attack, saying that it had conducted more than 400 interviews with people in the San Bernardino area.