WASHINGTON (REUTERS) - The couple who massacred 14 people at a California holiday party were discussing jihad and martyrdom online a year before they met in person, but there is no evidence that Islamic militants arranged their marriage to facilitate an attack, Federal Bureau of Investigation (FBI) director James Comey said on Wednesday (Dec 9).

The FBI believes Syed Rizwan Farook, 28, the US-born son of Pakistani immigrants, and Tashfeen Malik, 29, a Pakistani native he married in Saudi Arabia last year, were each inspired by Islamic extremists before they became acquainted, he said on Capitol Hill.

The precise origins of the couple's indoctrination in extremist ideology remain to be determined but appear to date back about two years, before the Islamic State in Iraq and Syria (ISIS) "became the global jihad leader that it is", Mr Comey said.

"They were actually radicalised before they started dating each other online, and as early as the end of 2013 they were talking to each other about jihad and martyrdom before they became engaged," the FBI director testified before the Senate Judiciary Committee.

The husband and wife were killed last week in a shootout with police hours after opening fire with assault rifles at a holiday gathering of Farook's co-workers at the Inland Regional Centre social services agency in San Bernardino, about 100km east of Los Angeles.

Fourteen people were killed and 21 others were wounded in the Dec 2 assault, marking the deadliest burst of US gun violence in three years.

Mr Comey has said the FBI is investigating the mass shooting as an act of terrorism. If the investigation proves the massacre to have been the work of killers inspired by Islamic militants, as the FBI suspects, it would mark the most lethal such attack on US soil since Sept 11, 2001.

He said both the couple had declared that they were carrying out their attack "on behalf of" ISIS, an assertion he said they made "at or about the time" of the killings.

The FBI previously cited a pledge of allegiance Malik was said to have made on Facebook to ISIS, the militant group that has taken over parts of Iraq and Syria and claimed responsibility for attacks in Paris last month that killed 130 people.

A US government source has said Farook may have been plotting an attack as early as 2011, while a second government source said he may have looked at a number of potential targets.

Mr Comey said it would be "very, very important to know" if their marriage had been arranged by a militant group as a way to carry out attacks in the United States, although he said there was no evidence yet indicating that.

In response to a question from Senator Lindsay Graham, Republican of South Carolina, Mr Comey acknowledged that evidence of Islamic extremists playing such a role in their marriage would be "a game changer."

FRIEND AND RELATIVE

The investigation of Farook and Malik has also focused on his relationship with his boyhood friend Enrique Marquez, a Muslim convert who federal officials said made a 2011 or 2012 purchase of the two assault-style rifles used by the couple in the attack.

A government source familiar with the investigation said the authorities were trying to determine if Farook had asked Marquez to buy the two rifles so as not to draw attention to himself.

Marquez, who worked at a Walmart Supercentre in Corona, California, has not been arrested in the case, but he was questioned by the FBI on Tuesday (Dec 8) and his family home was raided over the weekend.

Marquez checked himself into a Los Angeles-area psychiatric facility soon after the shooting.

State marital records examined by Reuters revealed that Marquez' wife and the spouse of Farook's older brother are sisters.

CNN, citing unnamed US officials, reported that Marquez had told investigators he and Farook conceived an attack in 2012 in California, but they abruptly abandoned the plan, in part because they were spooked by unrelated FBI arrests around that time of four people charged with attempting to travel abroad to carry out jihad.

The San Bernardino Sun newspaper quoted investigation sources as saying multiple photographs of Carter High School in Rialto, California, were found on Farook's phone.

Mr Gasser Shehata, a friend of Farook's from a San Bernardino mosque, said Farook told him several years ago that Marquez had converted to Islam.

On his marriage certificate, Marquez and his wife listed their religious society/denomination as Islamic Society of Corona/Norco.

VISA QUESTION

Republican members of the Senate Judiciary Committee grilled Mr Comey about the attack and criticised the Obama administration's response to ISIS.

The committee's chairman, Republican Senator Charles Grassley, said the San Bernardino shootings had shown President Barack Obama to be "spectacularly wrong" about the security of the US visa screening process since Malik arrived in the United States on a K-1 fiancee visa on which he said she listed a false address.

"Our government apparently didn't catch the false address in Pakistan that she listed on her application," Mr Grassley said.

Mr Comey said in response to a question that he has no reason to believe the ISIS already has cells in the United States.

"They are trying to motivate people already in the United States to become killers on their behalf and they would very much like to - as they aspire to be the leader in the global jihad - send people here to conduct attacks," he said.

He added that the latter scenario "has not been seen yet".