In a new essay entitled Proof the FBI Changed Documents, and Vincent Bugliosi Was Wrong, Pat Speer traces the history of an important finding which casts a question mark over the sanctity of the documentary record in the JFK assassination case.
The focus of the essay is a pair of FBI memos regarding tests made on a paper bag recovered from the 6th floor of the Texas School Book Depository (TSBD). In one memo, tests of paper taken from the TSBD's shipping area showed it to have "the same observable characteristics" as the paper bag, and this has been cited as evidence that Oswald fabricated the bag himself and brought the rifle into the TSBD in it.
But in 1977 researcher Gary Shaw found at the National Archives an almost identical memo, with the same date, in which tests showed the bag “not to be identical” with TSBD paper. In this essay, Speer retraces the work of Shaw and others, and finds the explanation offered by author Vincent Bugliosi to explain this discrepancy wanting. He also presents an FBI memo directing that all copies of a report featuring the "not to be identical" memo have that page replaced with the alternate version; proof that the FBI was not above altering its own reports after the fact.