I would say the key to the exculpatory evidence for Lee Oswald is the negative result of the Dallas Police paraffin test for gunshot residue on his right cheek.
This negative result was confirmed by the Atomic Energy Commission Oak Ridge Laboratory, which also tested seven men who did in fact fire a Mannlicher Carcano and who all tested positive.
This information was available to J. Edgar Hoover Director of the Federal Bureau of Investigation as shown in Gerald D. McKnight, Breach of Trust: How the Warren Commission Failed the Nation and Why.
Further, the shot at Walker involved two men who drove off in separate cars; Lee (whatever John Armstrong may posit) was not two men, nor was he typically described as a driver.
The Walker case is even worse, as Edwin Walker loudly protested that the bullet in evidence had been switched from the original 30.06 to a Mannlicher Carcano 6.5.
The Tippit killer was not Lee Oswald per Aquila Clemmons who was threatened by two armed white Dallas Police to keep quiet if she wanted to avoid harm.
The witness who talked to the dead officer and could not identify Oswald until led into it by counsel, Helen Markham, was considered a basket case by government officials.
Lee Oswald was not even associated in any way with the alleged weapon per Gil Jesus’ 10 Reasons http://www.jfklancerforum.com/dc/dcboard.php?az=show_mesg&forum=3&topic_id=85804&mesg_id=85804
Lee Oswald was an intelligence operative for ONI, CIA, FBI whose last call alive was Saturday night November 23, 1963, to John Hurt in North Carolina, his ONI handler.
He was at no time a Communist, nor did he renounce his citizenship; his “defection” was one of two dozen such contrived events part of a program of false defectors. One of these was Robert Webster of Rand Corporation whose Leningrad address was in Marina’s address book.
Marina was a prime agent in the posthumous framing as was Ruth Paine whose sister was CIA and who had a relationship with Allen Dulles. Dulles was in Ft. Worth in the weeks prior to the assassination.
Indeed Ruth’s agency with Marina and Lee is central to maneuvering the patsy into the Depository at the time of the motorcade.
For a fresh look at Lee Oswald, see Judyth Vary Baker, Me & Lee.
John Newman, Oswald and the CIA, 2008 revised edition, demonstrates the manipulation of Oswald’s file and the Mexico City creation of the World War III virus so necessary to insuring the cover up.
At every turn the intelligence officer is used to attack the pro-Castro Fair Play for Cuba Committee, while the official propaganda takes the cover at face value.
A young Marine working covertly on behalf of his country is cynically murdered and slandered for assassination by the very agency he served.
Such is the state of the Cold War still conducted under the current iteration of “national security,” a twilight zone where the president may now seize and imprison—even murder—any citizen without warrant in blatant violation of the Fourth Amendment.