How do we know that terrorists did not claim responsibility?? If the government doesn't want that info made public, we don't find out.
Example: Everyone knows that Oswald ordered a rifle through the mail using a fake name. (and then carried an I.D. under that name.) In Texas, 1963, the only way that a purchased rifle could be traced to you, is if you ORDERED IT THROUGH THE MAIL!!
So, the government wanted you know something about the so called assassin's rifle. But they only wanted you to know the damaging info, not the exculpatory facts or facts that seem to point toward a conspiracy.
“...taxes are not raised to carry on wars, but that wars are raised to carry on taxes”
Thomas Paine, Rights of Man