Some questions: Did they call the bomb squad? Evacuate the school? Put the school in lockdown? Put the bomb/clock in a safe area until they knew for sure it wasn't a bomb? Transport the bomb/clock in a safe or appropriate vehicle? The answer is No to every question. So, they knew it wasn't a bomb. Then why do this? The only answer is that they wanted to intimidate Muslims in their district. Basically tell all of them, in one action: You are not welcome and we are watching everything you do.