The FLIR video in "Waco - Rules of Engagement" makes a fairly good case that those trying to escape out the back of the building were machine-gunned.
The FLIR tapes are undeniable - federal personnel exited the tanks and fired at the back of the building.
There also was brass discovered from the FBI sniper posts at the back of the building. (Lon Horiuchi?)
A blue ‘ribbon commission’ (John Danforth) declared the machine gun fire to be sunlight reflection is the worst attempt at a white-wash in decades. The findings were so absurd that it actually proved the opposite of their conclusions.