Investigators believe San Bernardino shooter Syed Farook may have been plotting an earlier attack in California with someone else, CNN reports, citing two US officials.
One of the officials told CNN on Tuesday the two conspired in 2012 and a specific target was considered. Neither of the officials could say how serious the plotting got, CNN said.
One official said the two decided not to go through with the earlier attack after a round of terror-related arrests in the area, CNN reported. "They got spooked," the official said.
CNN did not give the name of the other plotter.
Meanwhile the FBI is investigating a loan of about $US28,000 ($A38,850) given to Farook and his wife Tashfeen Malik by an online lender and the man who supplied the guns to the couple.
The money was deposited into their bank account about two weeks before the attack, sources said on Tuesday.
Disclosure of the unsecured loan Farook, 28, took out from San Francisco-based Prosper, a peer-to-peer lending service, offered a new glimpse into the money trail under scrutiny by investigators of last week's mass shooting.
Investigations into assaults branded as acts of terrorism often focus on the money behind them and US government officials said the FBI's examination of the couple's finances has not linked them with any foreign group.
Still, one government source told Reuters that Farook and Malik apparently followed a pattern set by other militants who drained their bank accounts and exhausted credit lines before embarking on what they believed would be a suicide mission.
Fox News first reported on Monday that a deposit of $US28,500 was made into Farook's bank account from WebBank.com on November 18, and that Farook converted $US10,000 into cash, which he withdrew from a Union Bank branch in San Bernardino around November 20.
Fox also reported at least three $US5000 transfers were made in the days before the shooting, apparently to Farook's mother.
In addition to the pair of assault-style rifles and semi-automatic handguns the couple carried on the day of the killings, they were found to have amassed thousands of rounds of ammunition, along with explosives and other materials for making as many as 19 pipe bombs, according to the FBI.
Enrique Marquez, a onetime friend and relative by marriage of Farook, was questioned on Tuesday by US officials who said he had purchased the two assault rifles used in the attack, according to a federal law enforcement official.
Marquez was married last year to Mariya Chernykh, whose sister is the wife of Raheel Farook, the shooter's brother.
The family connection, revealed in marriage documents seen by Reuters, adds another element to the relationship between Farook and Marquez.
The FBI has described Farook, the US-born son of Pakistani immigrants, and his Pakistani-born wife Malik, 29, as a couple "radicalised" by Islamic extremist ideology.
Malik, who spent a good portion of her life in Saudi Arabia and married Farook there before returning with him to California in the (northern) summer of 2014, is believed by investigators to have pledged allegiance on Facebook to the leader of the militant group Islamic State just before the killings.
Malik's extremist views took form before she came to the US, but it remains to be seen whether she and her husband were indoctrinated by other individuals or whether they turned to radical ideology on their own, the FBI has said.
Authorities say the heavily armed couple opened fire on Farook's co-workers from the county Environmental Health Department during a holiday party at the Inland Regional Center social services agency in San Bernardino, about 100km east of Los Angeles.
Fourteen people were killed and 21 others were wounded in the assault. The couple died several hours later in a shootout with police.
Share
