Almost two decades after the fall of the Berlin Wall in November 1989, the actions of the communist government still fascinates and scares Germans. Who worked with them? And why?
Stasi employees started to destroy their secret files as the Berlin Wall fell. Initially they shredded them. But as the machines broke down under the strain, they were forced to tear documents by hand.
The waste was to be pulped or burnt, but "citizen committees" stormed Stasi offices across East Germany, seizing millions of files, along with 15,500 bags of torn-up documents.
"One of the main reasons why the citizen committees occupied Stasi offices was to prevent the destruction of these archives," said Andreas Petter, a chief archivist at the office now responsible for their preservation.
Since 1995, experts working near Nuremberg in Bavaria have been sifting through the bags, extracting the torn shreds, strata by strata, and taping them back together to reconstruct the documents.
"On average, a worker gets through about a bag a year," said Joachim Haeussler, another archivist.
Bags contain 3,000 pages on average, ripped into 12 to 15 pieces, and some 400 bags have so far been dealt with, accounting for about 900,000 pages or three percent of the total volume.
Initially up to 45 people worked on the project, but "it's clear that with just nine people now involved, it's going to take a long, long time to reconstruct the contents of all the 15,500 bags," said Petter.
But help might at hand in the form of a computer system which digitally recreates hand-torn and machine-shredded documents.
The German parliament last year voted to spend just over €6 million (nearly $10 million) on a two-year project which, according to its director, Bertram Nickolay, an engineer at the Fraunhofer Institute in Berlin, will allow the reconstruction effort to be completed in five to six years.
The digital system simultaneously scans both sides of the torn documents before comparing shapes, colour and pattern of script to work out how they fit together.
Four hundred bags have been sent to the Fraunhofer Institute for the project, and "testing of original material started just a few weeks ago," said Nickolay.
"We have learnt a lot from the people who do that by hand," he added.
"About 90 percent of the content of each bag comes from the same material" so the machine, like the people sifting by hand, tackle the shreds layer by layer, much as would an archeologist.
"We find bits that quickly fit together and what is left stays in the system to be compared with new pieces," said Nickolay.
"It's the biggest puzzle in the world," he added with pride.
In addition to speed, the computerized system should also allow for reconstruction of documents torn into very small pieces.
"One in five bags cannot be processed manually because the bits are too small," according to the engineer who said some pages were torn into 50 to 60 pieces, "suggesting they contained really explosive material".
Recreating the documents "is important to bring back to life what the powers-that-be of the time thought should best be done away with," said Petter.
Reconstructed material has already allowed some Stasi informers to be uncovered, said Petter pointing to one Heinrich Fink, a theologian who spied on both the Church and his students when he taught at Berlin's Humboldt University.
After the fall of the communist regime, Fink was appointed to head the university and was elected to parliament. His past caught up with him in 1995 when his file was finally pieced together.
Many documents still waiting to be reassembled likely deal with spying by the Stasi in the final years of the regime, not only against the political opposition at home, but against targets abroad, according to Petter.
Some other Stasi files were secretly whisked away by the CIA after the fall of the communist regime. They were only returned to Germany in 2003.