Help with money problems with my Dad?

Okay, my dad went on vacation over a month and a half ago to visit his relatives there. Before he went however, he withdrew around $800 dollars from the bank in cash, kept it in a roll, and hid it in his room. Now that he's come back, he can't find the money at all.

Since he can't find it, he blamed me for stealing it and keeps insisting that I'd return the money to him, that he wouldn't be mad and assured me that he'd forgive me as long as I returned it. He even tried to guilt trip me by saying that he needed the money to pay his bills.

Here's the problem, I DIDN'T TAKE IT. For that matter, I didn't even know he kept money in his room until after he announced that it had went missing.

Although I admit I had a money problem back 6 years ago when I was 13 and in my first year of high school. I was foolish and wanted pocket money, so I resorted to taking money from my parents' wallets, mainly my mother's. However, I did stop after a couple weeks when my parents confronted me about it and started giving me an allowance. Then I got a job as soon as I was sixteen and didn't need an allowance anymore.

But now I see that my mistake has come back to haunt me. But seriously, I didn't take it since I have no need for it. I've saved up plenty of money in my accounts that I can spend however I wish, and I don't buy much except for the occasional run to the drug store for gum and snacks.

How can I convince my dad that I didn't take his money? I considered looking for the money so I could prove that I didn't take it, but I'm afraid that I'd still be accused of stealing it if I present the money it to my father, or be accused of putting it back where it came from if it was 'found' in an obvious place. And honestly, my dad is a forgetful person, I'm not really surprised that he lost it, he really should have just kept it in the bank.

I tried to tell my dad that perhaps that he had just misplaced it, but he won't believe it. Even my brother agrees with me on this, and knows that I didn't steal it. Mainly because he knows that I'm not retarded enough to steal $800 dollars in one go instead of slowly taking money to avoid attention and suspicion (like he had done in his youth except he wasn't caught and eventually stopped as well).

Please help me.