Is ender a murderer?

This all depends if we consider what happens in war to be murder. Really the death of Bonzo was accidental but the anaialation Buggers was orchestrated for the "good" of mankind. So yes, Ender did murder people and perhaps an entire alien race. Does he fit the popular colloquial definition of a murderer? I would say probably not. Remember, it's all about how we perceive things. One man's war hero can be another man's terrorist.