FBI agents work outside a home in connection to the shootings in San Bernardino, on Dec 3, in Redlands, California. A heavily armed man and woman opened fire Wednesday on a holiday banquet for his co-workers, killing multiple people and seriously wounding others in a precision assault, authorities said. Hours later, they died in a shootout with police. (AP)

SAN BERNARDINO, California, Dec 4, (Agencies): The woman who carried out the San Bernardino massacre with her husband had pledged allegiance to the Islamic State group and its leader on Facebook, a US law enforcement official said Friday, providing the strongest evidence to date that the rampage may have been a terrorist attack. The official said Tashfeen Malik made her posts under an alias and deleted them before she and husband Syed Farook killed 14 people Wednesday at a holiday party for his co-workers. The Muslim couple were killed hours later in a fierce gunbattle with police.

Malik, 27, was a Pakistani who came to the US in 2014 on a fiancee visa. Farook, a 28- year-old restaurant health inspector for the county, was born in Chicago to Pakistani parents and raised in Southern California. Another US official said Malik expressed “admiration” for the extremist group’s leader on Facebook under the alias account. But the official said there was no sign that anyone affiliated with the Islamic State communicated back with her, and there was no evidence of any operational instructions being conveyed to her.

CNN, quoting officials, earlier said Farook had been in contact with known terror suspects overseas and had become radicalized after marrying Malik in Saudi Arabia last year, although an imam at a local mosque he attended said Farook showed no signs of that. The Times reported that the FBI had evidence Farook had communicated with extremists domestically and abroad a few years ago. The two officials were not authorized to discuss the case publicly and spoke on condition of anonymity.

The FBI has been investigating the shooting at a social service center as a potential act of terrorism but had reached no firm conclusions as of Thursday, with authorities cautioning repeatedly that the violence could have stemmed from a workplace grudge or a combination of motives. Separately, a US intelligence official said on Thursday that Farook had been in contact with known Islamic extremists on social media. Law enforcement officials have long warned that Americans acting in sympathy with Islamic extremists — though not on direct orders — could launch an attack inside the US The Islamic State in particular has urged sympathizers worldwide to commit violence in their countries.

Farook had no criminal record and was not under scrutiny by local or federal law enforcement before the attack, authorities said. Friends knew him by his quick smile, his devotion to Islam and his talk about restoring cars.

They didn’t know he was busy with his wife building pipe bombs and stockpiling thousands of rounds of ammunition for the commando-style assault Wednesday on a gathering of Farook’s colleagues from San Bernardino County’s health department. “This was a person who was successful, who had a good job, a good income a wife and a family. What was he missing in his life?” asked Nizaam Ali, who worshipped with Farook at a mosque in San Bernardino. Authorities said that the couple sprayed as many as 75 rounds into the room before fleeing and had more than 1,600 rounds left when they were killed. At home, they had 12 pipe bombs, tools to make more explosives and well over 4,500 rounds, police said. Police Lt Mike Madden, one of the first officers to reach the room, said the carnage was unspeakable, the scene overwhelming: the smell of gunpowder, the wails of the wounded the blood, fire sprinklers going off and fire alarms blaring. All in a room with a Christmas tree and decorations on every table.