> In the spring of 1599, the trial was begun before a commission of the Roman Inquisition, and, after the accused had been granted several terms of respite in which to retract his errors, he was finally condemned (January, 1600), handed over to the secular power (8 February), and burned at the stake in the Campo dei Fiori in Rome (17 February). Bruno was not condemned for his defence of the Copernican system of astronomy, nor for his doctrine of the plurality of inhabited worlds, but for his theological errors, among which were the following: that Christ was not God but merely an unusually skilful magician, that the Holy Ghost is the soul of the world, that the Devil will be saved, etc.

He also has the interesting distinction of being excommunicated by three major denominations (the church of rome, the lutherans, the reform church, and elizabeth/CofE didn't like him much either) which is possibly a unique distinction for his time.

tl;dr: bruno had a seriously abrasive personality, heterodox and incoherent theological views, and the result wasn't pretty. His science, such as it was, had little to nothing to do with it.

[0]http://www.newadvent.org/cathen/03016a.htm