If a prosecutor had the opportunity to put on trial Lady Macbeth for being an accomplice to Duncan´s murder, what might his arguments be? (apart of Macbeth´s letter to Lady Macbeth)
His or her main argument should be that Lady Macbeth is the mastermind behind the murder's premeditation. I'm not sure about Scottish law, but in most civilized nations, a person who plans a murder such as hiring a hit man or forming a group to kill someone is just as liable as the person who "pulls the trigger."
The lawyer should also stress that Lady Macbeth was a very active participant in the actual murder. She tampers with evidence and creates a situation which is optimal for Duncan to be murdered.
Finally, Lady Macbeth basically admits her own guilt in the murder by her hand wringing and washing and her conflicted conversations with Macbeth.