The big question: why did he kill?

The verdicts delivered yesterday condemned constable Tsui Po-ko as a killer. Criminologists said he was a serial murderer who killed to gain a sense of excitement and power. But did the two-month inquest answer the big question: why did he kill?

Tsui, was found to be responsible for killing Leung Shing-yan after snatching his police revolver in March 2001, then launching another shooting attack in which he killed constable Tsang Kwok-hang and wounded Sin Ka-keung in a Tsim Sha Tsui underpass last year.

He was also blamed for the Tsuen Wan Hang Seng Bank robbery in December 2001, mercilessly killing a security guard, Zafar Iqbal Khan.

Police investigations revealed that he knew none of the men. The five-member jury was unanimously convinced that Tsui carried out all the crimes.

During the hearing, several experts - including an FBI official, criminologist, psychiatrist and psychologist - attempted to analyse Tsui's character and psychological state in the hope of understanding his motive.

FBI official James McNamara said Tsui had displayed seven out of nine notable symptoms for so-called schizotypal personality disorder. The disorder causes a pervasive pattern of social and interpersonal deficits marked by acute discomfort with close relationships, perceptual or cognitive distortions and eccentric behaviour.

He said Tsui was a suspicious and paranoid man who had no close friends or confidants apart from his immediate family.

Mr McNamara said Tsui craved excitement in criminal acts that was absent from his police work. He said the constable had no financial motives and was simply trying to attempt the impossible.Australian criminologist Roderic Broadhurst suggested Tsui acted out of frustration at not being promoted and joining elite taskforces.

He labelled the constable - who had spent 13 years in the force - as an 'unusual' serial murderer who killed to regain a sense of power.

'Through the control and humiliation [Tsui] passed onto the victims, he probably demonstrated his sense of authority,' he said.

Both experts relied on the written testimonies of Tsui's colleagues and supervisors handed to them by the police and sought to find justifications for Tsui's criminal motive.

But their eyebrow-raising conclusions failed to convince some interested in the case - including criminologist Dennis Wong Sing-wing, City University's associate professor of social sciences.

He questioned the validity of the FBI official's suggestion that Tsui turned to crime to attempt the impossible. 'Tsui was a calculated person,' Professor Wong said. 'Instead of saying that he wanted to attempt the impossible, he chose the subjects, the places he was familiar with. He knew what he should do in a familiar environment. He also knew how the police officers and security guard would react.'

Professor Wong said cultural differences and the limited scope of evidence available to them were the major limitations of their analyses.

'The information the experts had relied on was all from the police. They did not understand Chinese culture either,' he said, adding it was not uncommon for people in Hong Kong to satisfy at least half of the nine indicators for schizotypal personality disorder.

But is it really impossible to understand Tsui's character and his criminal motive when he is dead?

David Ho Yau-fai, senior consultant of the University of Hong Kong's centre of behavioural health, said it was feasible to build up a picture. The key was to gather as much information on the person as possible.

'The opinion of others on the person can be a reliable source [for personality profiling] because when most people make a similar comment about a person, it is probably right.' Dr Ho said. However, conflicting diagnoses from experts were quite common because a human being was by nature complicated.

'Different observers usually have different observations.'