Berger knew he was taking a big risk and therefore there had to be something worth "dying" for, just what it is we will never know.
Exactly.
Burgler did NOT go to take those documents just to review them.
He had a major NEED to erase something from historical reference. This could very well be it - not "erase A-D documents" but mention of A-D itself and the fact that Atta was mentioned by them.