This is the moment a brave San Bernardino cop reassured terrified workers at the scene of the massacre that he would protect them.

The unnamed police officer told cowering workers: 'I'll take a bullet before you do - that's for damn sure' as he led them through the bowels of an under-siege conference center.

They had been hiding inside the city's Inland Regional Center, where not long before Syed Rizwan Farook, 28, and his wife Tashfeen Malik, 27, burst in on a holiday party and opened fire with automatic weapons.

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Call of duty: The unnamed San Bernardino police officer, left, reassured terrified workers inside the besieged conference center (right) that he would protect them in footage filmed by one of the employees

The shooters began their massacre at the Inland Regional Center (top left) before fleeing. Police later traced them to a home in Redlands (bottom right), where a chase began which ended on San Bernardino Avenue (top center), where the two were shot dead

Local news footage shows one of the dead attackers outside the shot-out SUV. The suspect was killed in a police chase while still inside the vehicle, then moved on the street

Some of the wounded victims are pictured outside the conference center after the shooting

Attacker: Killer Syed Farook is pictured here in an image he uploaded to a dating website

The policeman had been tasked with getting the group of several dozen people out from the building safely while there were still concerns the gunmen could be inside, ready to strike.

In an attempt to help the people get out quickly and safely, the unnamed officer says: 'Try to relax, try to relax. I'll take a bullet before you do, that's for damn sure.'

After several twists and turns inside the center, the policeman asks the crowd to put their hands up before loading them on to a waiting bank of elevators, from where they were able to escape.

The video was recorded by Gabi Flores, a services worker inside the building, who later released the footage to the media.

Syed and Malik escaped the conference center before cops could stop them. They were traced to an address in Redlands, an adjoining city, which led to a dramatic police chase.

The couple drove their black SUV through the streets of San Bernardino, shooting and throwing fake pipe bombs from the back of the vehicle as they did.

The pursuit ended after police killed both attackers in a stand-off on a residential street.

On Thursday, police revealed just how well prepared the couple were.

Federal authorities said the two assault rifles and two handguns used in the violence had been bought legally, but they did not say how and when they got into the attackers' hands.

One woman lies one the floor as her colleague wails in tears in the makeshift treatment center

They fired as many as 75 rifle rounds at the SUV scene and had had over 1,600 more bullets with them.

They also left behind three rigged-together pipe bombs with a remote-control device that apparently malfunctioned at the center.

At their Redlands home they had a further 12 pipe bombs, tools for making more explosives, and over 3,000 rounds of ammunition.

Wearing military-style gear and wielding assault rifles, they slaughtered 14 and wounded 21 in the attack at a social service center shortly after Syed slipped away from an employee banquet he was attending there.

As the FBI took over the investigation, authorities were trying to learn why the couple left behind their 6-month-old daughter and went on the rampage - the nation's deadliest mass shooting since the Newtown, Connecticut, school tragedy three years ago that left 26 children and adults dead.

'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,' said David Bowdich, assistant director of the FBI's Los Angeles office.

At the White House, President Barack Obama said after meeting with his national security team that it was 'possible this was terrorist-related' but that authorities were unsure. He raised the possibility that it was a workplace dispute or that mixed motives were at play.