The FBI Complaint, for one.

  ... I know that, on May 24, 2013, a Silk Road user sent
  him a private message warning him that "some sort of
  external IP address" was "leaking" from the site, and
  listed the IP address of the VPN Server.

The Footnote labeled 4, bottom of page 28.

http://www1.icsi.berkeley.edu/~nweaver/UlbrichtCriminalCompl...

edit and off-topic rant: I really hate searching government PDFs.