If the slave is a murderer, and both buyer and seller are aware of the fact, there shall be no right of restitution for the purchase; but if the buyer acted in ignorance he shall have a right of restitution as soon as he realizes the situation, and the case should be tried before the five youngest Guardians of the if the vendor is judged to have known the facts, he must purify the house of the buyer under the Expounders' rules and pay him three times the price.