Original Posting document

Contract account 1000 was billed from January 2009 - March 2009. The customer moved to another location and all balances were transfered to the new contract account 2000. After another 3 months, the customer moved again to another location and all balances were transfered to the new contract account 3000.

Some of the customer's outstanding balances in contract account 1000 finally end up in contract account 3000 because of balance transfers.

How can I get the original line item that were posted in contract account 1000 for the balance transfers that's already in contract account 3000? I tried to use table DFKKOP but the clearing document (field AUGBL) does not indicate the line item.

Thanks.