The Washington massacre gunman used a valid security pass to get inside the navy complex where he killed 12 people but the motive for the shootings was still a mystery, investigators said.

The defence contractor who fatally shot 12 people at the Washington Navy Yard was carrying three weapons during the rampage.

At least 13 people died during a shooting at the Washington Navy Yard yesterday.

The man accused in a shooting rampage at a US navy base has been identified as a man from Texas.

A gunman has reportedly killed several people, wounding up to 10 others, and is still on the loose at a US Navy centre in Washington.