Going from memory here, but weren't some marks that are visible on the Carcano in the photos matched with marks on the Carcano that was found on the sixth floor?
Yep, the HSCA expert proved beyond all doubt that Oswald's rifle(C2766) that was directly linked to the fragments discovered in JFK's limo and found on the 6th floor of the Depository where Oswald worked, was being held by Oswald in the backyard of Oswald's apartment on Neely Street!
Also consider that Oswald lied to the Dallas Police that he lived on Neely Street, Hmmm I wonder why?
Another interesting factoid is that the backyard photos were taken shortly after Kleins sent C2766 and just before Oswald used C2766 in an attempt to assassinate General Walker.
The HSCA evidence that the backyard rifle was the murder weapon and consider that after more than 40 years later this evidence has never been even remotely debunked!

JohnM