Last Updated Dec 8, 2015 6:49 PM EST
SAN BERNARDINO, Calif. - Syed Farook got a $28,500 loan from online lender Prosper not long before the San Bernardino shooting, officials have confirmed to CBS News.
Farook and wife Tashfeen Malik stormed a holiday party for the office where Malik worked, killing 14 people with semiautomatic rifles and other guns.
Investigators have been working on figuring out the financial activity of Farook and Malik before the attack. The loan revelation has been among the trickle of details leaking out from the sprawling investigation.
Among the other details recently revealed by investigators, sources tell CBS News the attack on the center appears to have had a "blend" of motivations. There is evidence of a workplace grudge, but the FBI also said Monday it appears the pair had been radicalized for some time.
"The question we're trying to get at is how did that happen and by whom and where did that happen? And I will tell you right now we don't know those answers," said David Bowdich, chief of the FBI's Los Angeles office.
Malik expressed radical Islamic views even before she entered the U.S. on a fiancé visa in 2014, and continued after she arrived. Sources tell CBS News she was expressing those views since 2013 on her Facebook page. She talked about the negative treatment of Muslims around the world.
A U.S. official tells CBS News that it is believed that both shooters pledged their allegiance to the ISIS leader in the Facebook post by Malik - she posted under an alias.
Newly released emergency radio transmissions from the fast-moving tragedy show that police identified Farook as a suspect almost immediately, even though witnesses reported that the attackers wore black ski masks.
An unidentified police officer put out Farook's name because Farook had left the luncheon "out of the blue" 20 minutes before the shooting, "seemed nervous," and matched the description of one of the attackers, according to audio recordings posted by The Press-Enterprise newspaper of Riverside.
It is clear that the two had been planning for something. The couple had practiced at local gun ranges just days before the attack.
Farook signed in at Riverside Magnum Gun Range target practice with his AR-15, two days before the San Bernardino massacre. Mike McGee says Farook approached him at the range with a question.
CBS News' Carter Evans spoke with McGee who said when he met Farook, nothing about him stuck out. Farook had asked McGee a question when his gun began smoking.
McGee said the question, "Tells me that it was a new rifle. He was not familiar with it."
Farook practiced with an AR-15 semiautomatic rifle, the same kind of gun both shooters used in the attack, in addition to a pair of handguns. Authorities also discovered 19 pipes in the couple's home in Redlands, California, that could be turned into bombs. The FBI previously said it had found 12 pipe bombs.
If Farook had a particular grudge at work, it could have been related to what his father described as an "obsession" with Israel.
He said his son told him about tensions with a Jewish colleague at the San Bernardino County Health Department.
Nicholas Thalasinos was among the 14 killed in the Inland Regional Center massacre. His wife Jennifer said her husband, a Messianic Jew, was vocal about his support for Israel.
"He did know the shooter. He worked with him in the same department. They were both health inspectors," Jennifer said. "Knowing my husband, if there was something said or if he came in being very radical, I'm sure my husband had plenty to say to him."
In addition to apparently targeting coworkers, investigators have been examining whether or not the couple planned on carrying out other attacks in the area.
CBS News senior investigative producer Pat Milton reports law enforcement officials are also now scouring surveillance cameras at various businesses and sites in the region after someone said they spotted the attackers' rented black SUV in a nearby shopping mall the day before the shooting. A source said that it us unknown whether the shooters were scoping out the venue for an attack or stopped to shop, or just drove by.
Just before their rampage, Farook, 28, and Malik, 29, dropped off their 6-month-old daughter with relatives, saying they had a doctor's appointment. Farook's sister is now trying to adopt the girl, who is in custody of California child welfare services, and a custody hearing was held Monday.