If they have video of the incident I don't see how it could be anything other than "evidence".
I'm pretty sure the whole purpose of a jury trial is to weight all the evidence before coming to a decision.
Of course it is a liberal stronghold so that may not apply in all cases.
From what I read at the time the charges are valid in that the ranges own rules, as well as possibly federal laws were violated, since the "instructor" who was supervising the boy was only 16.