Law enforcement officials are attempting to discover what led a couple to shoot and kill 14 people at a social services centre in San Bernardino.
Tashfeen Malik, 29, and her husband Syed Rizwan Farook, 28, left their six-month-old daughter with Farook’s mother before perpetrating what is thought to be the worst mass shooting since 26 were killed in Newtown, Connecticut, in 2012.
Malik was killed alongside her husband four hours later in a shootout with police.
On Friday, the FBI said it is beginning to investigate the shooting as an “act of terrorism” as it was revealed Malik had pledged allegiance to Isis in a now-deleted Facebook post.
The FBI has acknowledged knowing little about Malik. It is unclear when she became radicalised, or who radicalised her.
FBI officers have indicated she and Farook probably “self-radicalised” online.
Authorities discovered a huge arsenal of guns, ammunition and pipe-bombs in the couple’s home, suggesting they had been planning additional attacks.
It has been reported Malik moved to Saudi Arabia with her father at a young age, and lived there until 2007.
She is then believed to have returned to Pakistan to attend a pharmacology school at Bahauddin Zakariya university.
An intelligence official said she was a “good student with no religious extremist tendencies”. She did not work as a pharmacist in the US.
Malik and Farook met in 2013 on the annual pilgrimage to Mecca, The Guardian reports.