He says he will be ‘forever haunted with guilt’ after school staff were not told about Cornick’s threats against the popular teacher.
One of his friends, now aged 16, told the Daily Mirror anonymously: “I don’t think about it as much as I did. I try not to. But I do still feel guilty because If I’d told someone, she would be alive today! I could have stopped it.
“I didn’t tell the teachers because I really never thought he would do anything.
“I thought he was just trying to scare us. I thought it was bravado - just a sick, terrible joke. I just thought it was a teenage thing.
“If I’d believed him for a second, I would have told someone.”
Corpus Christi Catholic College’s head teacher Stephen Mort wrote on the school’s Facebook: “There have been no threats, rumours or reports of threats or concerns about violence against school staff made by or concerning William Cornick made to the school.”
During the teenage killer’s sentencing earlier this year, it was revealed that he had told at least six of his classmates about his plans to kill Mrs Maguire.
He was jailed for 20 years after slaying his teacher in front of a classroom of students earlier this year.