Why did they leave him alone? Big Mistake!

in the end they made a huge mistake of letting him go into his room alone ANGRY and close the door leaving him alone with his demons. They should have hired a police officer to follow him around or had a camera in his room to see what he was doing at every second. Heck they video recorded everything else! he was telling them what was to come, what they didn't believe he'd actually go through with it?