Powerful investigation tool: A Police officer demonstrates how to take a swab sample.

It isn't uncommon for culprits to murder and rob their victims, then flee - leaving no clue or fingerprint for crime-busters. But Police officers can now make use of a powerful investigation tool to track them down.

Officers at the Force's Identification Bureau and chemists at the Government Laboratory work hand in hand to use DNA - deoxyribonucleic acid - to piece puzzles together to find clues to unsolved crimes.

DNA examination has become an even more effective forensic device since the Police Force (Amendment) Ordinance took effect in July 2001.

The legislation empowers the Police to take DNA samples from suspects, people convicted for serious arrestable offences and volunteers for identification purposes.

DNA identification is expressed in terms of probability, such as having a one in 10 million chance that two unrelated people will have the same profile. It is therefore practically unique and quite safe to be considered as admissible evidence in courts of law.

Still, it is preferable to use DNA evidence when there is other, non-genetic evidence to be considered alongside it.

The Government Chemist, on behalf of the Force, maintains a DNA database of key DNA information under stringent controls.

DNA effective in detecting serious crimes

Chief Inspector William Ho said DNA examination has become an effective crime-solving tool for the Force and proven to be particularly useful in detecting crimes such as murders, chain burglaries, kidnaps and sexual offences.

"So far, we have successfully identified a substantial amount of matches of DNA samples. The result is really encouraging," he said.

Criminals sometimes flee without leaving any clues behind. With the advance of technology, police officers can look for DNA samples at crime scenes and compare them with other DNA information in the database.

"After DNA comparison, it is probable that we can find a link among different cases and the data may even suggest that a particular person has been present at the crime scene. This brings tremendous help to us and provides evidence of a suspect's involvement or innocence," he said.

Mr Ho said most suspects who had kept on denying their involvement in a crime confessed soon after DNA test results made it clear that they were at the scene.

Use of DNA more widespread

Government Laboratory Forensic Science Division Chemist Dr To Kwong-yuk said the use of DNA examination has become more and more widespread.

"In the past, we used to test DNA collected from crime scenes where body fluid like blood and semen were found. With the advance of technology, we can now analyse latent DNA that are invisible to the naked eyes."

Regarding the privacy of the persons from whom DNA samples are taken, Mr Ho said every step has been taken to protect the rights of sample subjects.

"After taking a buccal swab sample from a person's mouth, officers will seal it and attach a barcode label before taking it to the Government Laboratory for testing. The sample has to remain anonymous.

"Names, identity card numbers or other personal particulars and the corresponding barcode numbers will be kept in strict confidentiality by the Police's Criminal Records Bureau (CRB). The chemists have no access to such information.

"On the other hand, Police do not know the DNA profile of the person because it is kept separately in the Government Laboratory.

"The use of personal DNA profile is under stringent control by law to safeguard personal privacy and rights. Violation by anyone, even police officers, will result in criminal prosecution."

New techonology helps eliminate suspects

DNA is also an effective tool in eliminating suspects and in ascertaining the identities of dead bodies.

"From time to time, some people volunteered for DNA testing to clear their names," said Mr Ho.

Following the successful launch of the DNA database, the Force has plans to expand the scope and application of DNA examination to maximise the benefits of modern technology to detect crimes.

Starting in January, the Police began including more serious arrestable offences on the list of offences which are subject to DNA sample in accordance with the law. They include all dangerous drugs offences, firearms and ammunition offences and most of the offences under the Prevention of Child Pornography Ordinance. 

"We have also started reviewing old crimes cases which occurred before the DNA legislation took effect with a view to fully utilising the new technology. The latest DNA analysis methods are so advanced that they can produce a reliable DNA profile years, and even decades, after biological evidence were collected and stored, provided it was done properly," Mr Ho said.