John Mulchaey is portrayed by David Keith.
He interrogates everyone involved, who survived. These include Miss Desjardin, Sue Snell, Norma Bates and Jackie Talbot, who was involved in the horrible prank organised by Chris Hargensen and Billy Nolan. He also visits the places, where everything happened. Through his interrogations and investigations regarding the disaster we find out about the immediate aftermath of the destruction of Chamberlain, the harm that has been done, the number of deaths and the events described in the movie, which lead to the Black Prom.
Basically, the movie begins with his investigation and it is implied, he will be the man, who will come to realise, that Carrie White was responsible for the disaster, is still alive and will therefore also have the task of capturing her. The planned series, however, which would materialise this, did never happen.