The assault-style rifle used by a Santa Monica gunman to kill five people last week appears to have been put together using component parts.

Two officials briefed on the investigation who spoke on condition of anonymity say the semi-automatic weapon appears to be built with parts that are legal to obtain, but put together make the rifle illegal in California.

Investigators found a drill press in 23-year-old John Zawahri's room among other materials that indicate he likely assembled the weapon.

The drill press is used to help finish building the rifle by drilling holes in the lower receiver.

Zawahri was carrying 1,300 rounds of ammunition in magazines that were capable of holding 30 rounds each.

Such high-capacity magazines are illegal to purchase or transfer in California.