Orlando: Gunman's neighbor describes learning about Mateen US investigators on Tuesday worked to untangle the complicated motive of the "radicalized" gunman behind the massacre at a gay club in Orlando, as reports emerged that he frequented the popular nightspot and used gay dating apps. Omar Mateen, a 29-year-old American of Afghan descent, pledged allegiance to the leader of the Islamic State (IS) group in the midst of his killing spree, officials say -- the worst mass shooting in US history. IMAGES of the area where Mateen lived and SOUNDBITES from a neighbor