Police in California say the husband and wife attackers who killed 14 people at a work party in San Bernardino had 12 pipe bombs, tools for making explosives and more than 3000 more rounds of ammunition at their home.
But officials are no closer to discovering the motive behind the attack.
There was a hail of gunfire in a quiet suburb that killed both of the attackers. Mobile phone footage recorded the hundreds of rounds exchanged by police and the two individuals inside the vehicle.
It was quickly surrounded by armoured cars amid fears of booby-traps and explosives.
The suspects were identified as Syed Farook and his partner Tashfeen Malik, a husband and wife shooting team baffling FBI investigators.
Police had raced to the scene after the initial attack – to those watching from windows, it seemed like a drill.
An eyewitness told ITV News at first he hadn't realised the scale of what was happening.
Another employee captured the calm evacuation. A child was among those caught up in the terrifying events as workers feared they would be next in the line of fire.
But what of the motive? No one can say at this stage if the attack had connections to the Middle East.
Looking for answers, police overnight forced their way into the home of the suspects, just a few miles away from the scene of the attack.
Farook and Malik left their home heavily armed and with improvised explosives. But they also headed out with something else – their six-month-old baby who they dropped off with his mother on their way to launch the attack.
The brother-in-law of the main suspect said he was mystified by events.
The startling frequency of mass shootings and the very nature of this target – a Christmas gathering of local health workers – is proving deeply unsettling to ordinary Americans.
Breakfast TV shows this morning provided guidance and showed an official video on how to react if you find yourself caught up in such an event.
The bullet-ridden car of the attackers remains on the roadside, as the FBI grapples with the bigger question – is this a new form of terrorism, targeting the most improbable events to maximize fear?