Actually, if you read the article I linked to, her reason is because of his abuse (physical and other) and his forcing her to have an abortion. Not that those are reasons to sever his penis (him being "ruler of the house" and all), but that is what's stated in the report. She was declared not guilty by reason of temporary insanity and held in custody as a mental patient for a month, then released to receive ongoing outpatient treatment. He went on to become a porn star.
Does anyone remember how long OJ was in jail for slicing up Nicole?