DENVER (AP) — A man who killed his estranged wife and himself at a busy downtown Denver office building had become increasingly mentally unstable and was banned from a local airport for unspecified comments he made, police said Wednesday. The Tuesday afternoon shooting sent panicked office workers scrambling to escape the Alliance Center, a building that houses several environmental organizations and provides shared workspaces. Other downtown buildings were locked down, and people were warned to stay away from the area, which is steps from a pedestrian mall in the trendy LoDo neighborhood near a major transit hub and about four blocks from Coors Field.