A research team in Germany has developed a computer-software system to piece together some 45 million pages of secret police files ripped into 600 million pieces. The files were torn up nearly 18 years ago by panicking agents of communist East Germany’s dreaded State Security Service (Stasi), writes Ned Stafford in Nature‘s online news service.
The pieces of torn documents are scanned on both sides, and the digital images are then analysed by a cluster of 16 computers for 25 features, including colour, shape, texture, handwriting and typeface. Just like a person doing a jigsaw, the computer then groups the images into clusters with similar features, and finally fits pieces in each cluster together.
The torn documents date from the autumn of 1989, when the communist government of East Germany collapsed and jubilant West Germans and East Germans broke down the hated Berlin Wall. But not all East Germans were dancing in the streets. Stasi agents in ensuing weeks were holed up in offices around East Germany desperately trying to destroy evidence before West German authorities gained access to the files.
The Stasi lacked enough paper-shredding machines to do the job right, and began tearing documents by hand and stuffing them into bags. The plan had been to transport bags bulging with documents by trucks to locations where they could be burned, but by January 1990 East German citizens had taken control of Stasi offices and the plan could not be carried out. West German authorities eventually seized still-intact Stasi documents and more than 16,000 bags of ripped documents.