When Constable Leung Shing-yan was shot dead at a Tsuen Wan housing estate in 2001, DNA left on a surgical mask at the scene helped police link the killing to the 2006 Tsim Sha Tsui underpass shooting.
When serial rapist Cheung Shing attacked five young women after luring them into a stolen taxi outside Kowloon karaoke bars, again it was DNA that helped put him behind bars in 1996 for 24 years.
From a flake of dandruff to the saliva left on a postage stamp, the multiple ways people unwittingly leave a DNA trail has proven a curse for criminals and an invaluable tool for police forces worldwide. It has also solved immigration and paternity cases and identified victims of the 2004 tsunami.
Last week the man who pioneered the science that revolutionised crime investigation revealed the latest developments and predicted how DNA may be used in the future.
Delivering the Shirley Boyde Memorial Lecture at the University of Hong Kong, British geneticist Sir Alec Jeffreys spoke of how his unexpected discovery has swept the world, but also raised concerns that innocent people's DNA was being stored by police.
Sir Alec recalled the moment when the DNA identity concept dawned on him - 9.05am on September 10, 1984.
'That was a eureka moment. That was the moment when, entirely by accident, we came up with the idea that DNA fingerprinting was possible,' he said.
