I hate to be the bearer of bad news, but this just isn't the case; the buildings that 3CR occupies are old, to the tune of 30 years or so. There are no cameras in common areas, let alone the basement and arms rooms.
Where the Army does have cameras is in buildings that are currently being built; I know the new barracks for medics have cameras, and can be watched from the duty desk by the NCO on duty. I don't say this to be demeaning, but it seems like many people think cameras are wide-spread on military posts and that footage is readily available...unfortunately, it isn't. But believing that footage exists based on an opinion of how the Army works, then leads to angry thoughts of cover-ups and tampering, when in reality, there just isn't footage.
I say this just to ease your mind, as getting riled up right now in anticipation of the Army saying video was deleted does no good. If you know right off the bat that there aren't cameras, it can hopefully stop your mind from wandering down the path of how this investigation was botched or covered up. I lived and worked in these 3CR buildings; I assure you, there is no footage because there are no cameras installed in these buildings. That doesn't mean stop fighting the good fight and pressing for more answers, but this particular avenue leads you to a dead end.