Revealing mistake: There are bullets placed on the counter, the one casing has a hole in it from being drilled to show it's a dummy round and there's no gunpowder in it. (00:14:45 - 00:15:20)
Plot hole: The police are looking for school shooters who wore unicorn masks. There are cell phone recordings of the individuals shooting and I believe CCTV recordings from inside the school. There is a forensic science technique of accurately estimating suspect(s) height(s) using CCTV/camera recordings and math to determine the height. The police could have further narrowed down their pool of suspects by using this forensic method, but they are going at the students blindly chasing dumb leads.
