Shooter could just be a Fame seeker
If shooting was real and not staged by Tramp and his team then people may not understand that reason could be very simple - fame.
All those people see how every murderer of famous person or any big shooting is instantly immortalized by press and then Hollywood makes movies about them and actors get awards.
They still make shows about that guy who killed Lennon. Oswald is Hollywood legend. Guy who killed Lincoln. If he would kill Tramp - he would be immortalized the same. Constant movies, documentaries about his life and what drove him.