Why? Here is Last's summary of what the Thornburgh panel's typsetting expert, Peter Tytell, found:
Now, after careful examination, Tytell has come to three conclusions:
(1) The previously-released Texas Air National Guard documents had been created on an "Olympia manual typewriter."
(2) The four disputed Killian memos "were not produced on an Olympia manual typewriter."
(3) "The Killian documents were produced on a computer in Times New Roman typestyle."