The Army veteran suspected of killing four people at a Montana bar last week was still at large Sunday and may still be armed after escaping in a stolen vehicle containing clothes and camping gear, officials said.

Montana's Attorney General warned the suspect "is an unstable individual who walked in and murdered four people in cold blood for no reason whatsoever."

Police have found the getaway car of a US military veteran who walked into a bar in the western state of Montana on Friday morning and fatally shot four people, but the gunman remains at large.