Robert A. Frazier, an FBI ballistics identification expert, testified that he was “unable to reach a conclusion” as to whether or not the bullet recovered from Walker’s house had been fired from the rifle found on the sixth floor of the Texas School Book Depository Building. He concluded that “the general rifling characteristics of the rifle * * * are of the same type as those found on the bullet * * * and, further, on this basis * * * the bullet could have been fired from the rifle on the basis of its land and groove impressions.”[C4-732] Frazier testified further that the FBI avoids the category of “probable” identification. Unless the missile or cartridge case can be identified as coming from a particular weapon to the exclusion of all others, the FBI refuses to draw any conclusion as to probability.[C4-733] Frazier testified, however, that he found no microscopic characteristics or other evidence which would indicate that the bullet was not fired from the Mannlicher-Carcano rifle owned by Lee Harvey Oswald. It was a 6.5-millimeter bullet and, according to Frazier, “relatively few” types of rifles could produce the characteristics found on the bullet.[C4-734] Joseph D. Nicol, superintendent of the Illinois Bureau of Criminal Identification and Investigation, conducted an independent examination of this bullet and concluded “that there is a fair probability” that the bullet was fired from the rifle used in the assassination of President Kennedy.[C4-735] In explaining the difference between his policy and that of the FBI on the matter of probable identification, Nicol said: I am aware of their position. This is not, I am sure, arrived at without careful consideration. However, to say that because one does not find sufficient marks for identification that it is a negative, I think is going overboard in the other direction. And for purposes of probative value, for whatever it might be worth, in the absence of very definite negative evidence, I think it is permissible to say that in an exhibit such as 573 there is enough on it to say that it could have come, and even perhaps a little stronger, to say that it probably came from this, without going so far as to say to the exclusion of all other guns. This I could not do.[C4-736] Although the Commission recognizes that neither expert was able to state that the bullet which missed General Walker was fired from Oswald’s rifle to the exclusion of all others, this testimony was considered probative when combined with the other testimony linking Oswald to the shooting.