US police are on effort to establish why a man and woman fired openly at a social services centre in California, killing 14 people and wounding 17 more.
The pair, named as Syed Rizwan Farook, 28, and Tashfeen Malik, 27, were killed in an exchange of fire with police.
The mass shooting took place at the Inland Regional Center in San Bernardino, where Farook worked.
The FBI is investigating terrorism and a workplace grudge as possible motives, the bureau’s Los Angeles office said.
The incident marks the deadliest mass shooting in the US since 26 people were killed at a school in Newtown, Connecticut in 2012.
Farook and Malik are thought to be a couple with a six-month-old baby. Police said the attack indicated there had been “some degree of planning”.