How do "they" (and we) know? The FBI has the recovered forensic evidence and has apparently not given out any information.
Did the eight recovered shell casings match the rifle extractor/firing pin signatures? Were they all the same and were they all from the same rooftop recovered weapon? Were any test shots taken by the rooftop rifle afterwards to determine if cartridge/bullet marking characteristics were similar to any recovered fired bullets? Of the three people shot were any of these expended bullets recovered for evidence and forensic examination? Were any other expended bullets recovered from the scene for examination? Does everything match up? The FBI should have all that evidence unless they carelessly discarded it along with the body they quickly identified as "Crooks" (oops!).
And by the way, is the recovered body actually of Crooks? Does DNA and fingerprint examination match? Surely there was residual evidence in his home of this, at least, and it was searched that night.
Questions, questions,,,?
You raise points that should be part of the investigation, but as Clay Higgins said, the crime seen was removed be the FBI
We can only assume that the 8 casings were from the rifle.
I’ve heard a couple of good solid evidence of the ballistic audio, and they all say that the first 3 shots, followed by 5 shots had the same frequency, consistent with one gun. The you hear the 9th shot... and a few seconds later the 10th shot. Both from from different guns. So we have three guns.
Many unanswered questions.
Of the three people shot were any of these expended bullets recovered for evidence and forensic examination?
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One would think so but we’ll likely never know.