EXCLUSIVE - A $28,500 deposit was made to Syed Farook’s bank account from WebBank.com on or about Nov.18, some two weeks before he and his wife Tashfeen Malik carried out the San Bernardino massacre, a source close to the investigation told Fox News Monday.

Investigators are exploring whether the transaction was a loan taken out by Farook, who with his wife killed 14 and wounded 21 when they opened fire at a holiday lunch. He earned $53,000 a year with the county as an environmental health inspector. Investigators are also exploring the possibility that a subsequent cash withdrawal was used to reimburse Enrique Marquez, the man who bought the two AR-15 semiautomatic rifles used in the San Bernardino shootings. Marquez, who could be charged, especially if it is determined that he illegally modified the weapons, is now reportedly answering investigators’ questions.

“Right now our major concern at the FBI, the ATF, and the JTTF (Joint Terrorism Task Force) is determining how those firearms, the rifles in particular, got from Marquez to Farook and to Malik,” assistant special agent in charge with the Bureau of Alcohol, Tobacco and Firearms, John D’Angelo, told reporters in California Monday.

The deposit came via Utah-based WebBank.com, which describes itself as “a leading provider of national consumer and commercial private-label and bank card financing programs” on a nationwide basis. On or about Nov.20, Fox News is told Farook converted $10,000 to cash, and withdrew the money at a Union Bank branch in San Bernardino. Afterwards, in the days before the shooting, there were at least three transfers of $5,000 that appear to be to Farook’s mother.

The loan and large cash withdrawal were described to Fox News by the source as “significant evidence of pre-meditation,” and further undercut the premise that an argument at the Christmas party on Dec. 2 led to the shooting.

Fox News is also told that investigators are exploring whether the $10,000 cash withdrawal was used to reimburse Enrique Marquez, the man who bought the two semiautomatic rifles used in the San Bernardino shootings. Marquez is now reportedly answering investigators’ questions.

At Monday's news conference, authorities said the weapons were all legally purchased in California between 2007 and 2012.

The source, who was not authorized to speak on the record about the federal investigation, said there is further evidence of pre-meditation with a charge for the SUV rental processing on Farook’s account Nov. 30, two days before the shooting.

Contacted by Fox News, a woman who was identified by another employee as Lorie Gilbert and a member of WebBank.com’s strategic partnership, said they were “not going to respond to that (questions about the Farook transaction)” before hanging up. Another WebBank.com employee said they were “not talking to the press.”

A spokesman for Union Bank, David Weidman, declined to comment on specific questions, including whether the Nov. 20 $10,000 cash withdrawal triggered reporting requirements. Weidman confirmed they are working with the FBI and others, adding, "We are cooperating to the full extent of the law with the agencies conducting investigations into this tragedy.”

There was no immediate response from lawyer David Chesley, who has been representing the family.