It isn't uncommon that people get killed, valuables have been stolen and culprits have fled, leaving no clue or fingerprint for crime-busters. But nowadays, police officers can make use of a powerful crime investigation tool to track down the culprits.

A Scene of Crime Officer from Identification Bureau looks for DNA samples at a crime scene

DNA examination has become an even more effective forensic device after the Police Force (Amendment) Ordinance took effect in July 2001. The legislation empowers the Police to take DNA samples from suspects, persons convicted for serious arrestable offences and volunteers for identification purposes.

DNA identification is expressed in probability terms, e.g. one in 10 million chance that two unrelated persons will have the same profile. It is therefore practically unique and quite safe to be considered as admissible evidence in courts of law. That said, though, DNA evidence is still preferably considered alongside non-genetic evidence in a case.

The Government Chemist, on behalf of the Force, maintains a DNA database storing important DNA information under stringent control by provisions of law.

To understand the process of locating these "invisible" criminals, OffBeat invites Mr William Ho Siu-ting, Chief Inspector Crime Support and the Chemist at the Government Laboratory Forensic Science Division, Dr To Kwong-yuk, to review the implementation of the Ordinance.

Mr Ho said: "Since enactment of the new law, DNA examination has become an effective crime-solving tool for the Force and proven to be particularly very useful in detecting crimes including 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!"

Dr To, who has been carrying out DNA tests since 1998, said the success of the DNA database is obvious and is well above his expectation in view of the overseas experience, given the number of "cold-hits" of DNA samples.

Mr Ho said criminals sometimes fled the scenes without leaving any clue. With the advance of technology, police officers could 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 kept on denying their involvement in crime, confessed soon after the DNA test results were available and spoke for themselves.

Taking DNA samples

The DNA legislation requires that only trained officers can take non-intimate DNA samples from persons. While certified frontline police officers have been trained by Government Laboratory to take swabs from people's mouths, the important task of finding DNA samples at crime scenes is vested in the hands of veteran Scene of Crime Officers (SOCOs) from Identification Bureau.

At present, more than 1,000 frontline police officers from different regions and districts are holders of the Buccal Swab Sample-taking Certificate after being trained by Government chemists to take DNA samples.

Dr To 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."

Collection of samples for latent DNA tests requires a high degree of professional skill and judgment on the part of SOCOs.

Mr Ho said: "At the end of the day, we can't remove everything from a crime scene for forensic tests in Government Laboratory. This will only lengthen the time required for laboratory testing and create a backlog. The collection of DNA exhibits has to be selective, precise and professional.

"The Scene of Crime Officers - most of them having accumulated over a decade of experience in collecting evidence such as fingerprints from crime scenes - know where to look for such DNA samples."

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. He said: "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.

"Even if a chemist has made a successful matching of DNA samples, he only knows that a particular DNA sample from the crime scene matched with a barcoded sample taken from a person. Upon notification by the Government Laboratory, the CRB which stores the personal particulars and barcode information will inform the officers-in-charge of crime cases of the test results when they are out.

"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."

Stringent quality control

Manned by 12 chemists and more than a dozen of technical staff, the Government Laboratory in Ho Man Tin is responsible for testing DNA samples on exhibits collected at various crime scenes. Another laboratory in Lai Chi Kok, however, is mainly responsible for testing swab samples from humans.

In 2003, DNA crime scene sections at the Ho Man Tin Laboratory had all together examined thousands of exhibits collected from the crime scenes of more than 4,000 cases. The figure represented a 100 per cent and a four-fold increase compared with 2002 and 2001 respectively.

For setting up the DNA database, Government Laboratory has adopted the same procedures from the Federal Bureau of Investigation. To ensure local practices are up to par with international standards, they also attend international conferences to share their experience with experts worldwide.

The Government Laboratory, accredited by the American Society of Crime Laboratory Directors (ASCLD), follows a set of stringent procedures in the handling of DNA samples. Such procedures, inter alia, include measures to handle DNA samples from victims and suspects separately to avoid any contamination.

Dr To said: "After we have received exhibits from police officers, we shall select the most suitable laboratory test. We can compare DNA samples collected from different exhibits, or run the data in the database for matching.

"Apart from the computerised data comparison process, the chemist responsible for the case will also double check the test results again to ensure accuracy."

Testing DNA samples

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.

Dr To pointed out that DNA testing could sometimes be difficult, especially when the quality of the DNA sample itself is poor.

"Sometimes, the bodies of victims were found long after deaths. The bodies had badly decomposed or had been dumped in sea for some time. All these had complicated DNA testing and we have to spend much longer time in examination."

Talking about one of his most unforgetable experience in DNA testing, Dr To remembered a case in which a man's body was sealed with cement years ago. He had to overcome many difficulties in handling the exhibits and samples taken from the deceased.

"Through DNA testing, we were eventually able to locate the first scene of crime. The body had been taken there from where it was found."

Dr To said his work has given him and his colleagues great job satisfaction. "It's a rewarding job. DNA helps bring the offenders to justice and exonerate innocent people quicker than ever before. I am also pleased that we can help ascertain the identities of victims so that their family members can put their hearts at ease."

Future plans

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

Mr Ho said: "Starting from this January, we have included 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.

"Our long-term goal is to turn DNA sample-taking from a person into a general skill for police officers so that they may get the know-how soon after joining the Force or after receiving continuation training.

"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.

"We see the forensic DNA tests as a calling card in our arsenal of investigation tools because it is very difficult for a criminal to avoid leaving his DNA traces at scene of crime though he is aware of it," Mr Ho said.

Dr To Kwong-yuk explains the DNA interpretation process