Complex passwords and deniable file system seems to be the trick. (And a court system which cannot "compel" the owner to reveal the password.)
http://www.computerworlduk.com/techn...S&newsid=20900
Open source encryption stymies FBI hackers
TrueCrypt program defeats police dictionary attack
By John E Dunn ShareThis
The FBI has admitted defeat in attempts to break the open source encryption used to secure hard drives seized by Brazilian police during a 2008 investigation.