Nothing. In fact, he can claim anything he wants -- abducted by aliens, bushy haired stranger climbed in the window, food poisoning at an Albanian bistro, God pointed and she dropped dead, etc.
It all comes down to what a jury is going to believe.
Unfortunately, most juries that are selected are missing a key piece of evidence...their brains. The only ones that can serve on a jury for 4-6 months at a time are those diagnosed with Alzheimers and the unemployed who can't keep a job. These are the people making the decisions for the country on who goes to prison and who is freed. Pitiful.