Talk to the IT Department. They keep mirror copies of the daily image of the corporate collective database. This data is collected daily and archived on a massive scale for a variety of reasons including the potential for a 911 catastrophic event. Lehman may be a subscriber to the black mountain data storage system sponsored by a branch of the Federal Govt. in connection with the clearning house banks that serve the Treasury in various govt. bond trading operations. These have been deemed of national importance in the event of an attack. Coordinate your investigation with Homeland Security.