Syed Farook
Syed FarookReuters

The husband and wife who killed 14 people in last week's shooting rampage in San Bernardino, California were both radicalized "for quite some time," the FBI official in charge of the investigation said Monday, according to AFP.

David Bowdich, the FBI's assistant director in charge of the Los Angeles field office, said investigators were still trying to determine how and by whom Syed Farook and his wife Tashfeen Malik were radicalized before the December 2 shooting.

"But I will say this -- as the investigation has progressed, we have learned and believe that both subjects were radicalized and have been for quite some time," he was quoted as having said.

The couple had taken target practice at Los Angeles-area shooting ranges, and once "within days" of the massacre, Bowdich told reporters, according to AFP.

Farook and Malik left their baby daughter at home on Wednesday before heading to the Inland Regional Center in San Bernardino east of Los Angeles, where some of Farook's colleagues had gathered for a year-end party.

The couple opened fire, killing 14 and wounding 21 others. They were killed hours later in a firefight with police.

It is believed Farook had contact with people from at least two terrorist organizations overseas, including the Al-Qaeda-affiliated Al-Nusra Front in Syria.

On Friday, it was reported that Malik had pledged allegiance to the Islamic State (ISIS) in a Facebook posting.

And on Sunday, Farook’s father told an Italian magazine his son was “obsessed” with Israel, shared ISIS ideology and wanted to see the establishment of an Islamic caliphate.