Legal Question in Wills and Trusts in California

I'm sorry to hear about what must be very difficult circumstances. I'm not sure I understand the question--if your son was executor of his father's estate and took money from the estate, he would be liable for the money he took. If your son has now passed away, his estate would be liable, though his share of his father's could offset the money taken.

If instead he used a credit card of his father's after his father's death, it's possible he could have been charged with fraud, but at the least he would have been facing a civil suit from the bank to recover the amounts he charged on the card. If he has money in his own estate, the bank may pursue a creditor's claim to get its money back.