The contents of files of the former East German secret police, the Stasi - which were destroyed after the fall of the Berlin Wall - are slowly emerging after being pieced back together through new software developed in Berlin.
The E-Puzzler system, developed at the capital's Fraunhofer Institute for Production Systems and Design Technology, works by scanning the fragments of the documents into a computer image file.
Then, by treating each scrap as if part of a jigsaw, the information gathered by the notorious agency is being restored.
"It is the biggest puzzle in the world," Bertram Nicolai, head of the Security and Testing department at the Fraunhofer Institute, told BBC World Service's Digital Planet programme.
"The goal of the pilot project is the automatic, virtual reconstruction of 400 bags. It is very important for German history."
Almost as soon as the Berlin Wall fell in 1989 - signalling the end of Communism - Stasi agents set about trying to destroy their files, first with shredders, and then with their hands.
Within weeks, they had filled 16,000 sacks with 600 million fragments.
Two years later, following reunification, German officials started trying to recreate the files by hand - but it became clear it was going to take too long.
Then researchers came up with the E-Puzzler, and managed to get a government grant.
The system analyses shape, colour, texture and thickness of the paper, so that it is eventually possible to rebuild an electronic image of the original document.
"It will be a long job - but that's the interesting part," said the Fraunhofer's Jan Schneider.
"First we have to digitise all the pieces from the bags. This is done by a special high-speed scanning device.
"The next step is to segment the image itself from the raw scan - we need the outline of the pieces, pixel-wise, to perform the reconstruction process after that.
"Then all digitised pieces of paper are stored in the database. After that we reconstruct a lot of the descriptive features of the pieces."
The researches stress they do not read the files, only reconstruct them
However, at the former Stasi prison Hohenschonhausen, the main place political prisoners were held and subjected to torture, there are criticisms that the process has already taken too long.
"I think it comes a little bit late," said Hubertus Knabe, director of the memorial at the site, which is also a museum.
"Nearly 20 years after the fall of the Wall we start to reconstruct these Stasi files, which are really important: the most important files were the ones they destroyed.
"I am happy that now it is going forward, but it is late."