Selling jointly owned stocks?

Lets say stocks are held in a family trust where there are two trustees(my mom and dad), and my dad sells some stocks and takes the money made on the sale and instead of putting it in the trust he puts it in his own bank account(in just his name). Could my mom charge him with stolen property or something because she did not approve of the sale of the stocks, because she did not know about it and she found out the money was put in another account. Is there a way he can be held legally responsible?