Bullet holes coming down through the roof at a high angle, would be my guess.
There was a great deal of physical evidence in that building which would have shown the place to be a crime scene, and I fully believe, the Feds to be the perpetrators.
Randy Weaver, Gordon Kahl, and Koresh (and doubtless, others) could have all been arrested alone, in town or elsewhere, and without gunplay had the desire been there to do so. Instead, the agencies involved opted for grandstand raid and strongarm tactics designed to intimidate, which backfired.
That explains the destruction of evidence. What was the initial motivation for this assault?
I really don't think anything "backfired" at Waco. Reno was entirely too smug afterwards.