Blood spatter revealed story of constable's death to trained eye

Forensics expert Henry Cheung Kam-yin spent exactly a year examining a wooden door, but it was no ordinary piece of wood - it was splashed with the blood of fallen constable Leung Shing-yan, shot in the head and body five times by off-duty constable Tsui Po-ko when he responded to a noise complaint in 2001.

Dr Cheung, who worked in the government laboratory for 10 years before retiring three years ago, was entrusted with the task of analysing the blood spatter, attempting to extract any crucial information on how the brutal attack took place.

'The scene was the most complicated I have encountered,' said Dr Cheung, one of a dozen forensic scientists in Hong Kong to receive training in blood-spatter analysis.

'There was an incredible amount of evidence to look at - such as the DNA evidence and other items collected at the scene - apart from the complicated bloodstain pattern.'

Dr Cheung said it took him a year to compile a report on the forensic evidence of the case.

'I looked for more information from books, and synthesised various pieces of evidence. It was quite a wearying process,' he said.

From his observations of the blood spatter on the fire exit door and the adjacent floor - as well as a pool of blood beside Leung's head - Dr Cheung concluded the victim was probably shot in the head while he was lying down. He also suggested the attacker was squatting near the fire exit when he fired the gun.