You could only think that Sirhan Sirhan was "set up" and didn't do it by ignoring voluminous clear-cut evidence available immediately after the crime; the testimony of Rosey Greer ( famed football player and Kennedy bodyguard, who apprehended SS an instant after the gunfire stopped) as well as the many statements from Sirhan Sirhan himself trumpeting his great "triumph".
Generally a nut with a gun is a nut with a gun. Occum's razor cuts bull pretty well.