aaron alexis act alone. we are hearing the radio chatter of the first responders as all this began 24 hours ago. >> we have on the 4th floor a male with a shotgun. multiple shots fired, multiple people down. we'll give you an update on the building location. >> we have an officer down building 187 on the third floor. martha: people walking out of the building with their hand over their head afraid they will get shot if they appear to be anybody but themselves. alexis was a former navy h reservist. and no word on what the motive could have been for the shooting spree.