Laws exist to punish obviously bad behaviour (theft, murder, etc) while morals are made by society to tell you what's disgusting, what's lovey, what's fashion, what's cute, and so on.
Technically, laws exist to punish excessive deviance. Whatever "deviance" is is defined by the culture. As it turns out, in many places, certain loveual conduct (incest, homoloveuality, bestiality, child enthusiasm, etc) is considered deviant behaviour to the extent that the legal proceedings of a society punish individuals for taking part in them. From a sociological standpoint, criminal justice exists to uphold the morality of a society in such a way that deviance is punished, and the moral belief in the culture is affirmed through that punishment. Of course, that's not to say that morality needs law to be upheld; law is just a way that societies utilise government to punish deviance. And as I'm sure you'd be aware of at this point, bestiality is unfortunately considered taboo in quite a few cultures.