How did Neil get out of the toilet block after he shot Scott. The dean said that that coridor was the only way to the toilet block, and he didn't run past Harry. And he can't have climbed out the window or anything because he was evacuated out the front door.
Also, why did he (Neil) claim to have killed all of them when he knew it was Scott who did it? Was that just to scare Niki into doing what he said?
Not to mention all the surveillance cameras. Neil felt responsible for the murders because he didn't stop Scott. He was a crazy mixed up kid. Or some rot. It was all serious nonsense.
Basically the Nikki/Neil scenes were just one big disclaimer by the writer who exploited real events for sleazy suspense. Likewise Harry's "human nature" speech at the end about Jason saving the day. It was all deeply dishonest. The Beeb just doesn't want to be seen encouraging all the idiots out there. But campus shootings are a cult now and episodes like this won't help no matter how many disclaimers the producers plonk in.