Explosives, ammunition found at California shooting attackers' home

The two attackers who killed 14 people in a gun rampage in California fired up to 75 rifle rounds, left behind three pipe bombs and had over 1,600 more bullets with them when they were gunned down.

At their home, they had 12 pipe bombs, tools for making more explosives, and more than 3,000 rounds of ammunition, Police Chief Jarrod Burguan said.

Wearing military-style gear and wielding assault rifles, Syed Rizwan Farook, a 28-year-old county restaurant inspector, and his wife, Tashfeen Malik, 27, killed 14 and wounded 17 in the attack at a social service centre shortly after he slipped away from an employee banquet he was attending there.

The couple were shot to death about four hours later and a few miles away in a furious gun battle with police.

As the FBI took over the investigation, authorities were trying to learn why the couple left behind their six-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...