1. Check the public records to see if an address is listed for the lender. That office might still have the file or know where it went.
2. Contact the person who handled the sale. See if they have a contact person or know the lawyer who handled the bank's position.
3. Call a main number for WaMu and ask what office handles property that has gone back to the bank in that specific location.
4. Remember that the loan might have been sold as part of a bond pool. Who exactly owns the loan and therefore now owns the property might be unclear and not WaMu. Or WaMu might have received the loan back when the default happened given the bond pool terms and conditions.
You need to chase the details. Expect that most everyone you speak with will be paid by the hour or a salary but do not get paid to be all that helpful. This is one file. One property. If the details get lost none of the people on the phone will see a pay reduction. They will also not get a bonus if the property sells faster in most cases. Hence they are not going to be on top of their game when it comes to this one specific house. It is a number on a computer screen and not much more.
It might be worth your time but it certainly will be a rather painful experience most of the time. Painful in terms of frustration.
John Corey