Right to Left or Left to Right?

My friend and I were watching Law and Order. A man cut a woman's throat. The coroner said it was cut from left to right. My friend immediately said, we both watch this a lot, "That means he was left-handed!" I told her "No, it means he was right-handed!" We argued. If you watch a lot of crime shows, you might know this. If a throat is cut from left to right, does that mean the attacker was left-handed or right-handed?