If there was another shooter, there will be other bullets and casings found that won’t match the guns in Paddock’s room.
If the shooter was perched on either the inside of the Mandalay Bay sign, or on the towers across the street, a simple brass trap would prevent casings from flying. If it was a reflection, which i believe it was, as a strobe light would be consistent, then there are only two structures that could reflect the muzzle flash at that height. The sign, and the towers
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