By Mark McGregor
BBC News, Manchester
After a hard day at school Michael Hamer enjoyed coming home, retreating to his room - and pretending to be a teacher.
Prof Cooper says bullied children often internalise their pain
According to police, Hamer - who has been given a life sentence for murdering 11-year-old Joe Geeling - was fascinated by the younger pupils at St Gabriel's High, often creating his own school timetables using the names of those from years below.
For a 14-year-old who was badly bullied, recreating the school environment in his spare time may seem like a strange pastime.
But psychology professor Cary Cooper says such role play offers the perfect escape from the horrors of the daily ritual.
"If somebody pretends to be teacher when they get home it sounds like they are creating a fantasy world," he told BBC News.
"It's not necessarily a good way of coping with being bullied but it enables them to feel that they have some kind of control for a short period of time, even when they really don't."
Hamer was picked on at school in Bury, Greater Manchester. He was assaulted by pupils his own age and often had his dinner money stolen.
Police said teachers at St Gabriel's High handled the problem very well, excluding some pupils.
But it is how Hamer reacted to the violence and tormenting that ultimately may have led to him brutally taking Joe's life.
He told detectives that he wanted someone else to feel the hurt and pain he did when he was bullied at school.
Although all the evidence points to a pre-planned bid to get Joe into his house, Hamer claims he "just flipped".
Prof Cooper, of Lancaster University, says problems often occur when people deal with being bullied by internalising their suffering.
"The tension builds up and builds up and it's like a pressure cooker - it can explode," he said.
"Usually if it explodes it is with innocent people. People who are maybe as vulnerable as they are, or even more so."
"Taking it out on innocent people serves a function. They're saying: 'Okay, they're in control of me but I'm in control of them'."
While bullied children need to find an outlet for their frustration, it is very rare for it to transfer to extreme violence against another person, Prof Cooper says.
More often than not, the violence is turned on themselves in the form of self-harm or attempted suicide.
Violence against others does happen, the professor adds, but "not to the extent necessarily of them taking another's life".
"The person who has been bullied has been so dramatically bullied, so violently bullied, kept it so much to themselves and buried it that they have lost any sense of reality," he said.
"If it turns into violence against themselves or other people there is usually a trigger mechanism.
"Those cases involve a lot of suppressed anger which has to come out in some form or another.
"But to turn the violence gratuitously on somebody else, so violently that they take somebody else's life... it's very, very rare."
Cary Cooper, Professor of Psychology and Health at Lancaster University, recently led a national study into work-place bullying