Investigators in the US believe the woman who carried out Wednesday's gun attack in California with her husband had sworn allegiance to the so-called Islamic State.
It is claimed Tashfeen Malik had made the declaration on social media using a different name.
14 people were killed at a social care centre in San Bernardino.
Tashfeen Malik pledged allegiance to Islamic State and its leader on Facebook using an alias, then deleted the messages before the attack, officials have said.
She and husband Syed Farook killed 14 people at a Christmas party for his co-workers on Wednesday.
The disclosure about the online activities of Tashfeen Malik provided the first significant details suggesting the rampage may have been a terrorist attack.
Malik, a Pakistani, went to the US last year on a fiancée visa before she and Farook married in California. They had a six-month-old daughter.
Malik’s alias on Facebook and specifics about her postings were not publicly disclosed by law enforcement officials.
Malik reportedly expressed “admiration” for the IS leader on Facebook under the alias account, but there was no sign that anyone affiliated with so-called IS communicated back to her and no signs of any operational instructions being conveyed.
The FBI is investigating the shooting as a potential act of terrorism but has reached no firm conclusions. A US intelligence official said Farook had been in contact with known Islamic extremists on social media.
At the same time, law enforcement officials from local police to attorney general Loretta Lynch cautioned it could have been work-related rage, or a hybrid of religion and personal vendetta.
Farook, 28, had no criminal record and was not under scrutiny by local or federal law enforcement before the attacks. Friends knew him by his quick smile, his devotion to Islam and his earnest talk about cars he would restore.
They did not know he was busy with his wife building homemade bombs and stockpiling thousands of rounds of ammunition for a commando-style assault on a party of his co-workers that killed 14 and injured 21 in San Bernardino, California.
Authorities said the couple sprayed as many as 75 rounds into the room at a social care centre before fleeing. They died four hours later and two miles away during a furious gun battle with police.
The pair had more than 1,600 bullets when they were killed. Police said they also had 12 pipe bombs, tools to make more explosives, and well over 4,500 rounds of ammunition at home.
The dead ranged in age from 26 to 60. Among the 21 injured were two police officers hurt during the manhunt, authorities said. Two of the wounded remain in critical condition.
Nearly all the dead and wounded were county employees.
Farook was born in Chicago on June 14 1987, to parents born in Pakistan. He was raised in southern California.
In July 2010, he was hired as a seasonal public employee and served until December that year, according to a work history supplied by the county. In January 2012, he was rehired as a trainee environmental health specialist before being promoted two years later. Among his job duties was inspecting restaurants.
The soft-spoken Farook was known to pray every day at San Bernardino’s Dar Al Uloom Al Islamiyah mosque.
Fellow mosque goers said Farook abruptly stopped going to pray three weeks ago. Until then seemed happy and no one saw anything to make them think he was violent.
Farook told worshippers that he travelled to Mecca in Saudi Arabia last summer. They said he was gone about a month before returning to the US with his wife. Malik arrived on a visa for fiancées and with a Pakistani passport in July 2014, authorities said.
The two were married on August 16 2014, according to their marriage licence. Both listed their religion as Muslim. The couple had a six-month-old daughter who they dropped with relatives on Wednesday morning before the shooting.
Farhan Khan, Farook’s brother-in-law, told NBC News that he had started the legal process to adopt the girl. He described Farook as a “bad person”, but said he was not radical.
Farook legally bought two handguns used in the massacre and the two assault rifles were legally bought by someone else federal authorities wanted to question. That person’s identity was not released.
Details about his upbringing are sparse.
He grew up in a turbulent home but later graduated from California State University, San Bernardino, with a degree in environmental health sciences in 2010.
Divorce records depicted a home divided by abuse. Farook’s mother alleged in 2006 that her husband, also named Syed, attacked her while her children were present, dropped a TV on her and pushed her toward a car, according to records.