Investigators say they have yet to find a direct link between "Islamic State" and the San Bernardino attack, in which 14 people were murdered. But they added that it was being investigated as an act of terrorism.
Investigators said on Friday that they believe the female shooter in the San Bernardino, California killings had pledged her allegiance to the leader of the "Islamic State" (IS) jihadist group. Tashfeen Malik, 27, had posted an online statement of support for IS online under a false name, according to government sources.
A Facebook official said Malik had praised the leader of IS, Abu Bakr al-Baghdadi, in a post just as the first emergency calls came in from the shooting scene. The account has since been removed from public view. A law enforcement official said, however, that there was no sign that anyone affiliated with IS had communicated back with her.
The IS-affiliated news agency Aamaq said that the two shooters were "supporters" of the group but stopped short of claiming responsibility for the attack. A recent report from George Washington University said that 71 people in the US had been charged in connection with supporting IS since March 2014, including 56 in this year alone.
Investigation into act of terrorism
In the light of these findings, the FBI announced it was officially investigating the mass shooting in San Bernardino as an act of terrorism.
FBI Director James Comey stressed, however, that the investigation had not shown any evidence that the couple were part of a terror cell. He added that currently there was "a lot of evidence that doesn't quite make sense."
The police shared photos of the weapons used by the attackers, as they unearthed a sizeable arsenal at the couple's rented home.
"There is no indication that these killers are part of an organized larger group or form part of a cell. There is no indication that they are part of a network," he told reporters in Washington. The couple may have been planning an additional attack, he added.
Should the investigation prove that the attack was indeed inspired by militant Islamism, it would count as the most serious such attack since September 11, 2001.
Malik and her husband, 28-year-old Syed Rizwan Farook, left their 6-month-old daughter at her grandmother's before they opened fired at the Inland Regional Center, a social services agency in San Bernardino, about 60 miles (100 km) east of Los Angeles, on the evening of December 2, killing 14 people and injuring 21. They were then killed themselves in a shootout with police.
Co-worker: Farook 'married a terrorist'
Malik was a native of Pakistan who had been living in Saudi Arabia when she met Farook during his month-long vacation there. Malik had been subjected to vetting in order to get her US visa - a process the US government described as vigorous. It includes being checked against terrorist watch lists.
The other asssailant, Farook, was born in Illinois to two Pakistani immigrants, and was an environmental health specialist for the city of San Bernardino.
Initial reports indicated that the shooting at the city's Inland Regional Center occurred during a holiday party for county public health employees, and that Farook had left the party angrily earlier in the evening.
Christian Nwadike, who had worked with Farook for five years, told broadcaster CBS that his colleague had seemed different after returning from Saudi Arabia.
"I think he married a terrorist," Nwadike said.
Left behind a six-month-old infant
Police said that the couple had two assault-style rifles, two semi-automatic handguns and 1,600 rounds of ammunition in their car. A search of their home revealed 12 pipe bombs and 4,500 rounds of ammunition.
Farhan Khan, who is married to Farook's sister and has acted as a family spokesman, expressed his utter dismay at the couple's actions and offered his condolences to the victims' families. He announced that he had begun proceedings to adopt their child.
"You left your 6-month-old daughter," Khan said. "In this life, some people cannot have kids. God gave you a gift of a daughter. And you left that kid behind. (...) What did you achieve?"
es,ss/rc (AP, AFP, Reuters, dpa)