The shooters in the massacre in San Bernardino may have been radicalized. An American-born Muslim and his wife had allegedly been in touch with known terrorism suspects.
US intelligence officials reported that the San Bernardino gunman had been in contact with known Islamic extremists on social media. Details of the attack emerged as investigators tried to establish whether the rampage had been an act of terrorism.
Police said Farook and his wife had amassed enough bullets and bombs to slaughter hundreds when they launched their deadly attack on a holiday party at a social service center for the disabled, located in San Bernardino.
Wearing black combat gear, 28-year-old Farook, and his wife, Tashfeen Malik, 27, used 75 rounds of ammunition in the rampage that left 14 people dead. Four hours after the siege, the couple died in a gun battle with police two miles away, during which they fired another 76 rounds of bullets.
Authorities said the attack had been meticulously planned. David Bowdich, assistant director of the FBI's Los Angeles office, said: "There was obviously a mission here. We know that. We do not know why. We don't know if this was the intended target or if there was something that triggered him to do this immediately."
An act of terror?
According to an FBI official, who spoke on the condition of anonymity, the couple had never been on the authorities' radar before. Law enforcement officials quoted in The New York Times said that the FBI was treating the incident as a potential terrorist act, but added that it was far from reaching any conclusions.
US President Barack Obama said that a terror attack could not be ruled out in the case but reminded the American public that the facts had not been established yet.
"At this stage, we do not yet know why the terrible event occurred," said Obama.
"It is possible that this was terrorist-related, but we don't know. It's also possible that this was workplace-related."
The President, who has only a little over a year left in office, has repeatedly called on the Republican-controlled Congress to pass tougher gun laws in the US, after a constant rise in numbers of mass shootings across the United States in recent years.
A massive arsenal of weapons
The attack was the deadliest mass shooting in the US since the 2012 attack on the Sandy Hook elementary school in Newtown in the state of Connecticut, which had left 26 people dead, including 20 children. But the events in San Bernardino could have resulted in much more devastation.
Residents have come together to hold vigils for the victims of the worst mass shooting of the year so far
The couple left three pipe bombs with a remote-control detonating device at the social services center, which apparently had a malfunction. There were also more than 1,600 rounds of ammunition remaining in their rented SUV when they died of gunshot wounds.
At a house in the nearby town of Redlands, the two had another 12 pipe bombs and more than 3,000 additional rounds of ammunition, according to police statements.
Honoring the victims
Authorities identified the victims of the shooting as six women and eight men from 26 to 60. The majority were county employees and colleagues of Farook, who worked as an environmental inspector for the health department. Another 21 people were injured, including two police officers. Two of the wounded remained in critical condition.
Several vigils have been held in San Bernardino to remember the victims of the carnage.
The couple had a 6-month-old daughter who they dropped with Farook's mother before the shooting.
ss/ng (AFP, AP, dpa)