hey, actually i know a bit about finance law...
i have my own lawyer, i told him a bit about the situation here...

Money which is banked into an account with an unknown origin, or money which is received in bank from a unknown/mistransaction, can be refund by bank with the evidence of.
1. receipient admit the money is unknown origin.(or he doesnt know the source)
2. the person who bank the money have the proof of transaction.
3. lodge a police report
4. solve this problem with the bank.

You don't need to go and find the person yourself, police and bank can settle this issue for you as long as you have the proof of transaction( anyway, this is the how you use the receipt of transaction when you want to undo something).
money with an unknown origin can be classified as bribe...

if he admit that he posted out the items, he must have proof of postage(trace number etc)..if he failed to provide proof, then you can claim back all your money, or at least, dun let the bad guy to have to money, frozen his account until investigations done.

so, i guess i'll choose to frozen his bank account until he strave to dead...hahha