Orson Scott Card: Speaker For The Dead [1987] paperback

Three thousand planet-bound years have passed while Ender the star-traveller remains young. In that time his name has become anathema, for he is the one who killed an entire race of thinking, feeling beings. No other has been found – until Lusitania is discovered. The young race there offers mankind a chance to redeem the previous destruction. The only humans allowed near are trained xenobiologists. But once again there are tragic misunderstandings. And when Ender, as Andrew Wiggin, is called to Lusitania to speak for the dead – to present to the community the terrible truth of why men have been killed by aliens – his actions can, and will, reverberate through an entire galactic empire.