Investigators seek motives for worst US mass shooting since 2012

Investigators are searching for the motives behind why a husband and wife allegedly opened fire with military-style weapons killing 14 people and wounding 21 at a Christmas work party in California.

The two suspects, US-born Syed Rizwan Farook (28) and his Pakistani wife Tashfeen Malik (27), left their six-month-old daughter with Farook’s mother on Wednesday morning, claiming to have a doctor’s appointment, before launching their attack. Law-enforcement agencies are investigating possible terrorism and a workplace grievance as motives.

"It would be irresponsible and premature for me to call this terrorism," said David Bowdich, assistant director of the FBI in Los Angeles.

The mass shooting took place at the Inland Regional Centre, a state-run centre for people with developmental disabilities in San Bernardino, about 90km east of downtown Los Angeles.

Body armour

Farook, an inspector for a local county health department, had been at his work party and left “under circumstances that were described as angry”, said San Bernardino police chief

Jarrod Burguan

. Up to 30 minutes later, Farook is suspected of returning, along with his wife, to the party at about 11am armed with assault rifles and semi-automatic handguns and wearing masks and body armour.

A remote-controlled explosive device, made up of three combined pipe bombs, was left behind at the scene but failed to detonate.

The couple were killed more than four hours later after a chase of a rented black SUV spotted at the scene and a shootout with police.

Police said the couple had 1,600 rounds of ammunition on them or in their black SUV and later found 2,000 more rounds, 12 pipe bombs and hundreds of tools to construct more explosive devices at their home.

“There appears to be a degree of planning that went into this,” Burguan told reporters yesterday.

“Nobody just gets upset at a party, goes home and puts together that kind of an elaborate scheme or plan to come back and do that.”

The mass shooting was the deadliest in the US since a lone gunman killed 20 schoolchildren, six staff and himself at the Sandy Hook Elementary School in Newtown, Connecticut in December 2012.

Speaking at the White House, US president Barack Obama said: "It is possible that this was terrorist-related but we don't know. It is also possible that this was workplace-related."

Two of the four guns, the handguns, used in the attack were purchased legally by Farook, police said, but they declined to say who purchased the “long guns”, the two high-capacity assault weapons.

California has some of the toughest gun control laws in the country, which ban the sale or possession of many assault weapons, raising questions about how the weapons were obtained.

Saudi Arabia

Those who knew Farook, an American citizen, expressed surprise at his alleged involvement. Colleagues said he had recently travelled to

Saudi Arabia

and returned with a new wife, Malik, who he had met online.

His wife was living in the US on a “K-1” visa for fiancées.

Co-workers said Farook was a devout Muslim but rarely discussed religion at work. He had also travelled to Saudi Arabia, probably to attend the annual Hajj pilgrimage. The FBI said that Farook returned to the US in July 2014 and that he visited Pakistan.

“I just cannot express how sad I am for what happened today,” Farook’s brother-in-law Farhan Khan said at a press conference hosted by the Council on American-Islamic Relations on Wednesday night.

“I am in shock that something like this could happen.”