Generally, while you can keep them in restraints for pre-trial hearings, you have to take the restraints off for jury trials because it would keep the defendant from getting a fair trial if the jury saw what a bad dude he really was. Some jurisdictions are now using shock belts that you can hide under the clothes to control the really bad animals, but you generally can't parade them out in front of the jury in shackles and leg chains.
Of course, the person's right to a fair trial overrules security, even if they're the scum of the earth.
Err, "really"? Isn't that the point of the trial, to determine whether or not that's true?