Cho Seung Hui’s actions on Monday started with his intention to commit suicide, which he converted into a desire to seek revenge. He turned to violent movies to help him visualise the way in which he could carry this out, and having done so, he used the mass media to disseminate his message. I find it unsurprising that his actions reflect scenes from specifically violent films such as Oldboy and Face/Off. Film-makers create these films for their impact, but if an individual is mentally ill, this translates into a purely negative one. Movies don’t cause copycat crimes, but they do provide inspiration for them. Cho doubtless suffered from delusions of grandiosity, and adopted the type of behaviour of protagonists in films and computer games — he used emotive phraseology such as: “You love tearing my heart out and raping my soul”, despite being known for his silence.

The special effects and gratuitous violence seen in the mass media ultimately desensitise humanity, and Cho’s case illustrates how dangerous the repercussions can be. The way Cho killed one person after another, in some sort of reenactment of a mass slaughter, shows just how desensitised he was. There has been speculation that perhaps he killed himself because he realised the extent of his crime — that perhaps he had been gripped in a trance-like state. I very much doubt this. Crimes like this start with someone’s decision to commit suicide. Life is hopeless, and the way to give it meaning, to take control, is to take one’s own life. There is also a strong narcissistic element.

He associates himself with gods and martyrs. He refers to the crucifixion, and “martyrs like Eric and Dylan” – a reference to Eric Harris and Dylan Klebold, the teenagers who killed 12 students and one teacher at Columbine High School eight years ago today and who released a video in which they said they expressed their desire to be famous, discussing which director should ideally make the film of their forthcoming massacre — Spielberg or Tarantino.

The real question is whether the mentally ill blame themselves for life’s hopelessness or others. Cho blamed others. The differentiating factor depends on the type of illness and personality disorder suffered — does it stem from a paranoia, for example, or is it a more introverted type of depression. Often there is a paradox. The very thing that Cho rails against, namely the capitalism and hedonism of Western culture (“Your Mercedes wasn’t enough you, brats,” he said), is the thing that he is imitating in the first place. He filmed himself and sent the recordings to a news station — he wanted the attention the mass media would bring, and yet he blames this for his crime. This is not uncommon – what we hate the most in ourselves is often the thing with which we closely resonate. He could not live with the paradox, perhaps.

As a society, we would not spend hundreds of millions of pounds on advertising if we were not aware of the influence of the media, and hundreds of scientific studies suggest that when that translates into violence, then violent behaviour is increased, especially in the young. Along with civil liberty comes freedom in the press and consequently more collective risk as a society to monitor the vulnerable. That said, 100 years ago horrific crimes such as these took place — but the killers took inspiration from books rather than films, and there was no way for such crimes to reach a global audience.

Whatever is the cause of inspiration, those who feel rejected and vulnerable will turn towards compensation in the most grandiose manner to which they have been exposed. They want revenge, and in Cho’s case, it is the violent images he will have in his mind from the films he watched which fit his criteria, rather than the other way round.

There are often warning signs, false threats and pranks. Many young offenders I work with might attempt violence as a cry for help, but we have to take them all seriously. This creates a tremendous dilemma for school authorities and communities of course. The FBI and Secret Service studied the possibility of developing profiles of school shooters and concluded that it is not feasible. But both groups recommended threat assessment, involving investigating only those individuals who have communicated or engaged in some kind of threatening behaviour. Unfortunately, there is no federal funding for it and schools are forced to chose too often between prevention, security and academics.

Dr Dewey Cornell is a clinical psychologist and director of the Virginia Youth Violence Project at the University of Virginia