According to the defense motion, the Gitmo authorities have determined that only communications from counsel bearing their signature are legal mail. Any attachments (such as discovery, court opinions, expert witness CV's, news articles) attached to the letters are not and must go through a screening process which significantly delays the detainee's receipt of the material.

As the defense points out, historically all mail coming from counsel is legal mail which can be opened only in the presence of the inmate and checked for contraband and to ensure it really is from counsel. No further inspection is allowed:

See 28 C.F.R. 540.18.

a) The Warden shall open incoming special mail only in the presence of the inmate for inspection for physical contraband and the qualification of any enclosures as special mail. The correspondence may not be read or copied if the sender is adequately identified on the envelope, and the front of the envelope is marked “Special Mail—Open only in the presence of the inmate”.

As the defense argues, all mail coming from counsel is deemed privileged. The attachments reveal counsel's mental processes and legal strategy. There is no legitimate security reason to review this mail prior to delivery to the inmate.