Under the law you are 100% legally and financially liable for any deposits into your account
The first thing you have to do is file a police report against the person who sent the money. Bring the police copies of all emails, receipts, etc
Then bring a copy of the police report to your bank manager. The police report is the only way to show you were the victim of a scam, not the perpetrator. Without a police report the bank has no way to know you weren't trying to defraud them as every fraudsters tries to claim they are innocent
They may be investigating you for fraud, I am not sure that there will be forgiveness.
Sounds like a variation of a Nigerian 419 counterfeit check scam which you can find lots of literature on.
Some have suggested that fraud is the 3rd biggest national product in Nigeria, there was a pop song glorifying the practice "I Go Chop Your Dollar"
http://www.youtube.com/watch?v=f1nKR3gYR...
File a police report immediately against those fraud or scam to get rid of any risks.take all your documents and Emails copies with you. its the best option you can do .
Putting it into the bank was not too bright, but since it is not there any more you must have spent it. That was dumb. You will have to pay it off yourself.
you are totally screwed if you already sent out that $4800 to the scammer. You will be in serious legal trouble