In November, I went to a national toy chain to buy some Christmas gifts for my nephews. I wrote a check for the amount of the purchase but didn't have my drivers license, so the cashier wouldn't accept the check. I paid with my debit card, and the cashier "volunteered" to destroy my check. My statement came in December, and, to my surprise, this check appeared and was cashed. I called the store and they told me that the employee had been fired, but that they wouldn't refund my money. I called the bank, and they said that the endorsement was genuine, so they couldn't return the check. I filed a police report, but the suspect is long gone. How can I get my money back?

Can you tell who received the benefit from your check - the toy store or the employee? If the toy store, then they have been paid twice - which you can prove via your bank statement showing the debit card transaction.
If the employee, then filing the police report is pretty much your best option.
I'm sure you're beating yourelf up over this, but it bears repeating to other non-bank posters who might see this thread - the consumer bears the responsibility for destroying the private documents - don't leave it in the hands of someone you do not know - it's a hard lesson to learn, so learn from someone who has already experienced it and save yourself some grief.

However if you can show with the statement that the toy store and not the employee did get the funds I would certainly attempt that route again. If a direct approach does not work, depending on the toy store, perhaps a letter to the editor (or threat of such) to show that they do not back up the errors of their employees (albeit gone now) may pressure them to correct the error.

To start with, make sure you have a copy of the check. Your bank may offer this on-line or with your statement. Otherwise, order a copy from your bank. On the back of the check, verify who "endorsed" or signed the check. If the cashier cashed the check, it will likely be his/her signature. If the toy store deposited the item, then it will most likely have some sort of stamp in the endorsement area.

Good luck recovering the money.

Did you fill in the payee? If it was blank then you gave a signed check to somebody....and they cashed it.