How to return Bitcoins to sender through Bitcoin API? I want to get information about the creator of a given transaction through Bitcoin API. More specifically, any or all addresses they sent their Bitcoins from, so I can return some of the money back. Is it possible to do using just the JSON RPC, or do I have to rely on external sources (such as the Block Explorer)?
If the address is in your wallet, gettransaction includes the input addresses:


http://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list


If this is done by an agent where the addresses might not be in the wallet, v0.7 getrawtransaction gives you access to those transactions.


http://en.bitcoin.it/wiki/Raw_Transactions


There are other tools that you can use to build this capability as well.


libBitcoin
Armory (see Extras)
Bitcoin ABE