When visiting http://www.defcad.org, a message appears at the top of the screen.
DefDist Liberator Pistol: This file has been removed from public access at the request of the US Department of Defense Trade Controls.
Until further notice, the United States government claims control of the information.
A twitter post further confirms things:
#DEFCAD has gone dark at the request of the Department of Defense Trade Controls. Take it up with the Secretary of State.
— Defense Distributed (@DefDist) May 9, 2013