You are responsible because you cashed the checks at the bank. Because they were deposited, then turned out to be bad, your bank removed that money from your account -- just as they would have if you deposited a check that bounced.
You are now the one who can sue the person who sent you the phony moneygrams. Is sounds like you may have been the victim of a scam on eBay, Craigslist or another online shopping service. Phony buyers often send a person forged money orders or checks. Sometimes they overpay and ask the seller to send the difference back to them. There was even a scam where people were contacting florists, ordering a bouquet of flowers decorated with hundred dollar bills to be delivered to a guest at a hotel, and paying with stolen credit cards. Of course, by the time the credit card company charged back the fraudulent purchase, the crook was long gone from the hotel and the florist was out the flowers AND "decorative" money.
You can contact your local authorities about this scam. If the phony moneygrams came from overseas, you're probably out of luck.
Be sure to use Google to research any online program before you give them money.
You can 1) sue the people who gave them to you. You might take it up with the bank manager, telling them you were concerned and ask the bank to verify and they said okay, they can look up the teller and talk to the tell (it's all on the computer).
Was this part of a scam? Secret shopper, Nigerian, etc?
The question to ask our yourself is what did you give to get the money grams? That would help a lot.
Good luck with the situation. The above is general information and not legal advice since we don't have enough information as to all the facts.