The kooky website Cryptogon had a post a few days ago (hat tip: CQ) where they linked to an Immigration and Customs Enforcement strategic plan for detention and removal from 2004 codenamed Endgame. That report had previously been available online at ice.gov, but shortly after the Cryptogon post revealed its existence, it was removed from the website. The proprietors of this Cryptogon site therefore put it up on their own server, and you can download it here:
The document is unclassified and fairly banal, so I have a hard time believing that this was removed for security reasons. A likelier explanation is that it was removed because it was outdated, a lot of the content in it having been superceded by strategic work under the auspices of the Secure Border Initiative over the last 1+ years.