Schoolchildren in a bucolic region in western China famed for steam trains and jasmine flowers thought little of it when police interrupted classes and asked all the boys to spit into small plastic boxes.
They weren’t told why, according to the accounts of several children involved. From kindergartens through high schools, hundreds of male students were ordered to give enough saliva so that a filter paper inside each box turned from pink to white. The change indicated that the sample was sufficient for forensic scientists to extract the boys’ DNA, or unique genetic fingerprint. It would also identify biological traits common to blood relatives of each child.
The police in Qianwei County say their plan worked. They hoped the operation would offer clues to the unsolved murder of two shopkeepers nine years before, and soon they celebrated the murderer’s capture in state media.
An added bonus: The police collected a lot more names they could add to the world’s biggest DNA database, an essential part of China’s high-tech security blanket being unfurled across the country as Beijing seeks to better monitor its 1.4 billion citizens.
Nationwide, police have a goal of almost doubling China’s current DNA trove to 100 million records by 2020, according to a Wall Street Journal examination of documents from police departments across China. To get there, they need to gather almost as many records each year as are in the entire national database the U.S. has built over two decades.