It looked like a bomb and he was told by teachers to keep it put away. He even made the alarm go off in class. His father, a politician, turned it into an incident.
He experimenting hours and was proud of what he did. He wanted to show it to as many as possible, so he ignored what the teacher said. He was interrogated. Why more than one hour? It could have taken less then 10 minutes if you ask the teacher. Why was he handcuffed later? The police clearly wanted to make a statement or show.