Police officers investigating Wednesday's deadly shooting at a California centre for people with disabilities - say they've yet to find a motive for the attack.

The two shooters were killed after a shoot out with police in San Bernardino.

The incident has left 14 people dead and 21 injured.

Investigators have revealed they found a cache of weapons and ammunition when they searched the couple's home.

Local police chief Jarrod Burguan - says while they've yet to find out why the attack occurred - it was planned: