There is one video that shows four independent shots before the assault rifle shot almost like a countdown, wonder if this was so that several shooters could all fire rounds at the same time. In a test round, an assault rifle can only fire about 35 rounds in 10 seconds then has to reload, there are like 30 second rounds before a pause, that would indicate coordinated shooting of multiple assault rifles at once and explain all the weaponry in the room without all the casings.