Expert Asks Questions about Florida Shooting

The interviews where the kids say they saw "weird powder" and grey dust in the hallways is evidence of gunpowder and paper wad packing from blank bullets. Was this possibly a drill that went live? A possible scenario is while everyone was evacuating and hearing blank gunfire, during the panic and confusion operatives in the school misled and corralled some students and maybe a teacher in a room for safety and after everyone was out they executed them and anyone who may of accidentally been a witness was also taken out. At the least, the authorities knew the kid was going to go shoot up the school and did not intervene on purpose. Just brainstorming.... This not my actual belief. What say you?