The Jackass of Vanvres

In 1750, Jacques Ferron was caught having sex with an ass and sentenced to death.
To add insult to injury, the ass had a character witness:

The prior to the convent … and the principal inhabitants of the commune of Vanvres signed a certificate stating that they had known the said she-ass for four years, and that she had always shown herself to be virtuous and well-behaved both at home and abroad and had never given occasion of scandal to any one, and that therefore 'they were willing to bear witness that she is in word and deed and in all her habits of life a most honest creature.'

The ass was acquitted, and Ferron hanged.

Source: The Criminal Prosecution and Capital Punishment of Animals, 1906