I have found a way to disable automount in X-system:
Boot BT by using forensics mode
Execute "hostname bt5-forensics; exit" as root
As the system is setup to perform auto-login, after executing the exit command, the system will perform automatically a log in using the root user executing the /root/.profile script and in this case the if-clause for the forensics mode is executed (as it can showed in the console).
Finally when execute startx command to work with X-system, the USB driver are no automounted.
Is this the "normal" way to do it?