The closest thing to 'secret charges' is a secret indictment. This is a normal grand jury indictment, except its existence is not made public.

"Prosecutors may request a secret indictment if they are concerned that someone may flee if he or she becomes aware that trial proceedings are being set in motion. It is also possible to ask for one to protect witnesses and other people involved with the case. "

http://www.wisegeek.org/what-is-a-secret-indictment.htm