San Bernardino (California), Dec. 3 (The Telegraph): Investigators today hunted for clues why a married couple with a six-month-old daughter fired on a holiday party of his co-workers in California yesterday, killing 14 and wounding 17 before being slain hours later in a gunfight with police.

Officials said the FBI was treating its inquiry into the massacre by Syed Rizwan Farook, 28, and his wife Tashfeen Malik, 27 - both with Pakistani roots - as a counter-terrorism investigation.

An India angle has emerged too. Farook, an environmental inspector who joined the county health department five years ago, was registered on at least two online dating sites, including one for "Indian matrimonial and dating services".

Officials said the couple had stockpiled thousands of rounds of ammunition in their home as well as 12 pipe bombs, had travelled to West Asia, and that Farook had been in touch with people with extremist views in the US and abroad.

"It is possible that this was terrorist-related. But we don't know. It is also possible that this was workplace-related," President Barack Obama said.

Farook was born in Illinois to Pakistani immigrants, said Hussam Ayloush, head of the Council on American-Islamic Relations in Los Angeles. Malik was from Pakistan and was living in Saudi Arabia when she met Farook online.

An FBI official said the couple came to the US in July 2014 when they were not yet married. Malik arrived on a K-1 visa as the fiancée of a US citizen and on a Pakistani passport, and Farook did go to Pakistan at one point.

Officials said the attack may have also involved grievances against his co-workers with the county health department.

"You don't take your wife to a workplace shooting, and especially not as prepared as they were," said a senior law enforcement official.

"He could have been radicalised, ready to go with some type of attack, and then had a dispute at work and decided to do something."

Yesterday morning, the couple left their baby with Farook's mother Rafia at nearby Redlands city, saying they were leaving for a doctor's appointment, a relative said.

Farook then went to the party at the Inland Regional Centre, a social services agency, in San Bernardino, a largely working-class city of 220,000 people, 100km east of Los Angeles. He left "angry" after a dispute of some sort.

Farook returned with Malik around 11am and they fired on the celebration with two .223-calibre assault rifles and two semiautomatic handguns. The couple wore masks and body armour and placed three bombs at the scene, which police later detonated.

"There had to be some degree of planning," local police chief Jarrod Burguan said. "I don't think they just ran home and put on these tactical clothes."

When Rafia learnt of the shooting at Farook's work party, she was worried about him. Then she received a call - her son had been named as a suspect. Farook's brother-in-law said he had "absolutely no idea" why Farook would stage the shooting.# Ayloush said Farook's older brother had served in the US military. Co-workers said Farook was quiet and polite and did not bear any obvious grudges.

After the shooting, the couple fled in a black SUV. Late in the afternoon, police went to a house in Redlands and saw them take off again in a black SUV. They pursued the car to a site 2km from the massacre spot, where a gun battle left Farook and Malik dead.

'Normal' guy

Farook inspected restaurants, bakeries and public swimming pools for the county department.

Sue Ann Chapman, a waitress at China Doll Fast Food, which Farook had inspected this year, said: "He was real quiet. He checked the food and said he was here because somebody complained.... He looked completely normal."

Public records suggest possible turbulence in Farook's younger life. In 2006, Rafia had filed for divorce, citing domestic abuse by her husband. During one incident, she had said, her son came between them "to save me".

Officers said all four guns seemed to have been bought legally, two of them by a third person who has been taken into custody but may not have been involved in the shooting.

So far this year, the US has seen more than 350 shootings in each of which four or more people were wounded or killed.

Obama lamented an epidemic of gun violence that "has no parallel anywhere else in the world" and urged Congress to pass "common sense gun safety laws", including tougher background checks for firearm sales.

California has the strictest gun laws in the US that ban sale or possession of many assault weapons but there are loopholes.

Photo credit: The Telegraph