The recent arrest in Northwest China's Gansu Province of a confessed serial killer who is accused of raping and murdering 11 women between 1988 and 2002 has highlighted the vital role forensic science plays in catching criminals.
The key to solving the case lay in administering a Y-chromosome test to a relative of the suspect and comparing it with DNA evidence from a crime scene. The suspect's identity was finally confirmed through fingerprint checks and further DNA tests, according to statements made separately by the Gansu public security department and the Ministry of Public Security in late August.
Gao Chengyong, 52, was arrested in a grocery store in the city of Baiyin on August 26 after police used the latest technology available to them to re-examine Gao's DNA. Gao has since confessed to 11 murders, nine of which were committed in the city. The other two took place in North China's Inner Mongolia Autonomous Region.
City of terror
Baiyin, an industrial city that was built in 1956, was plunged into deep terror for years while Gao killed and raped women.
In 1998 alone, the suspect brutally murdered four women. The last killing took place in a hotel, which was only 50 meters away from a local police station.
Gao reportedly targeted young women dressed in red, raping them before or after the murder. He reportedly cut off the victims' reproductive organs.
While solving the case, the police encountered unexpected and great difficulties.
The western city had almost no surveillance cameras in the 1990s, and no direct or indirect witnesses could be found.
The crime scenes provided ample samples of blood, sperm, fingerprints and footprints, but police could still not locate the suspect.
Local police launched citywide investigations and made many of the city's men submit their fingerprints and DNA, but still failed to find the murderer.
The unsolved murders caused great panic among local women who dared not wear red or walk alone in the city's streets.
Gao continued killing women until 2002.
New technology
The investigation made no major breakthroughs for years until provincial police resumed the investigation by using new technologies this year, leading to the arrest of Gao.
Gansu provincial police said that they located the suspect through Y-chromosomal DNA test and the comparison of fingerprints.
The first breakthrough was when police found that a suspect surnamed Gao, who was then in detention over a minor crime, had a similar Y-chromosome profile to the serial killer. Police confirmed that the serial killer was related to this man after conducting more comparisons and tests.
Police then investigated his family members and finally determined that Gao Chengyong, the man's nephew, was the killer they had been looking for for two decades.
In recent years, genetic science has been widely used to solve criminal cases. But collecting suspects' genetic information is key for this to work, and suspects who are missing from the police's data bank have long been able to evade this kind of investigation.
The development of the Y-chromosomal DNA test technology helped solve this problem, as police can trace suspects without having their DNA on record.
It's known that all the men in a family share similar Y-chromosomes and what is known as Y-STR (short tandem repeat) information.
The chance of two men sharing the same male ancestor is 95 percent if four parts of their Y-STR information match. And if more than nine of their Y-STR match, this chance increases to 99.99 percent.
Analyzing Y-STR for forensic purposes started around 2001, only one year before Gao stopped his killings.
Zhang You, a biology PhD candidate, told The Beijing News that the Y-STR test can help police narrow down searches, especially after a Y-STR data bank is established.
According to a police officer at a public organ's DNA test center, the use of Y-STR technology by the authorities to build family data banks only began in recent years, as the project consumed lots of effort as it needed population censuses, investigations and the comparison of family trees, The Beijing News reported.
In the last few years, provinces and regions including Inner Mongolia, Henan and Zhejiang have launched Y-STR data bank projects.
The Baiyin case is the first successful application of Y-STR to solve a major case in China, providing an example for dealing with future cases.
