[Office of Legal Counsel] initially provided us with a relatively small number of emails, files, and draft documents. After it became apparent, during the course of our review, that relevant documents were missing, we requested and were given direct access to the email and computer records of REDACTED, Yoo, Philbin, Bybee, and Goldsmith. However, we were told that most of Yoo's records had been deleted and were not recoverable. [Former Deputy AAG] Philbin's email records from July 2002 through August 5, 2002 -- the time period in which the Bybee Memo was completed and the Classified Bybee Memo (discussed below) was created -- had also been deleted and were reportedly not recoverable. Although we were initially advised that Goldsmith's records had been deleted, we were later told that they had been recovered and we were given access to them.
That means the OPR investigators were without a key source of evidence as they weighed whether Yoo and others violated professional standards of conduct.
The Bush White House has also claimed to have deleted key emails. After good government groups sued, many of those will be recovered.