How do YOU prove that the government shot you dead, if they also shoot all the witnesses?
The government-ordered murders at Waco would have been easier to cover up if they hadn't made the mistake of letting the media put it out live on television. Think about how much more trust our government would have today, if they had just been smart enough to make sure there were no witnesses.
Destroying a computer is only different in degree - our Constitution makes either action illegal.