Authorities investigating the San Bernardino mass murder are focused on teasing out any associates, suppliers, trainers and financiers who may have helped Syed Farook and Tashfeen Malik mount their attack.
President Obama and other officials have said publicly that there is not yet any evidence that Farook and Malik were part of a broader conspiracy when they killed 14 people at a holiday office party, but investigators have not ruled out the prospect and are focused on the role of possible supporters.
In attempting to establish the scope of the attack plan and any inspiration or direction from international terror groups, the investigative team is examining a $28,000 deposit to Farook's bank account, data retrieved from cell phones and other devices, and a trove of paper collected from the couple's apartment.
They are also examining any electronic communications the couple may have had with people with extremist views in the U.S. or overseas, including possible contacts in San Diego and the Midwest. The couple was in touch in the past year with persons with extremist views in the L.A. area.
Officials have had difficulty retrieving information from the couple's cell phones because they destroyed them prior to the attack, and because some of the data from the phones was apparently encrypted.
Long-time Farook friend and neighbor Enrique Marquez -- who has been talking to authorities -- is of particular interest both for his role as a possible supplier of the assault weapons and for any information he could provide on a radicalization timeline.
NBC News has confirmed that a $28,500 deposit was made into a bank account belonging to Farook in the weeks before last Wednesday's attack. Farook's base salary in 2013 was $52,000. Fox News first reported on Monday night that the deposit was made from WebBank.com on Nov. 18.
Authorities are also interested in a number of people seen entering the garage at the Farook residence in Redlands, California in the months prior to the attack. Farook apparently used the garage as a bomb-making facility, and many bomb components were found in the garage after the massacre.
In addition, the Joint Terrorism Task Force had received information that a man resembling Farook sought access to a downtown L.A. office tower during the weeks prior to the attack and became agitated when denied entry. After examining information provided by the management of the office building, the FBI has concluded that the man was not Farook.