Disclosure of the unsecured loan the husband, Syed Rizwan 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.

Malik, who spent a good portion of her life in Saudi Arabia and married Farook there before returning with him to California in the 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.

Fourteen people were killed and 21 others were wounded in the assault. The couple died several hours later in a shootout with police.

If the massacre - the deadliest burst of US gun violence in three years - proves to have been the work of killers inspired by Islamic militants, it would mark the most lethal such attack in the United States since Sept 11, 2001.

In yet another twist to the case, state marital records examined by Reuters yesterday revealed that the man said by authorities to have furnished the couple with the two assault-style rifles used in the attack was related by marriage to Farook's family.

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