NEW : It 's unclear how Alexis got a shotgun past police . NEW : A Washington police officer ended the 30-minute spree by killing Alexis , mayor said . Alexis had served in the military and with police , but still had some issues . Authorities do n't know his motive , and police say they 're surprised by attack .
NEW : It 's unclear how Alexis got a shotgun past security . NEW : A Washington police officer ended the 30-minute spree by killing Alexis , mayor says . Alexis had issues in the Navy and with police , but still had security clearance . Authorities do n't know his motive , and friends say they 're surprised by attack .