In the centre of Stasi power the calendar still shows December 1989

BERLIN LETTER: They gathered in their thousands outside the drab, seven-storey office block in Normannenstrasse, East Berlin's most notorious address. The night air was icy but their rage was scalding.

"Stasi out! Stasi out!" chanted the rapidly swelling crowd as it pressed up against the entrance to the Ministry for State Security (Stasi) waving banners reading "The files belong to us."

The sweating Stasi employees inside thought otherwise. They had been methodically destroying files since the fall of the Berlin Wall two months previously. But now they had started working round the clock after getting a tip-off about the approaching demonstrators. They requisitioned as many shredders as they could and set to work destroying the information in the files so assiduously collected since the Stasi was founded in 1950 as the "Sword and Shield" of the Socialist Unity Party (SED).

The task was hopeless, mostly thanks to the Stasi's thoroughness: a quarter of a million full-time and part-time informers in a population of 17 million had created paper files filling 178 kms of shelves.

As the night of January 15th, 1990 wore on, the overworked shredders began to overheat and stopped working. Desperate Stasi workers started tearing up the files by hand. Anything to prevent the contents falling into the hands of the chanting mob outside.

At some point in the night, the protesters burst into the building and started surging through the corridors smashing everything in their path in the search for their files.

The files were East Germany's hottest property in the chaotic months between the fall of the Berlin Wall in November 1989 and German unification a year later. The storming of the Stasi headquarters marked the beginning of a bitter and dirty battle for control of these files.

The government of Helmut Kohl wanted them to be given to the National Archive and thus placed under the 30-year rule.

Meanwhile, the first and last democratically elected East German government agreed with the Citizens' Committee, the organisation occupying the Stasi buildings, to remove and destroy two million files of west Germans as well as transcripts of west German politicians' telephone conversations.

The legal battles dragged out over months: rooms sealed by the squatters were broken into during the night and files removed. Files supposed to have been destroyed turned up in the tabloids. Finally a government commission was established in October 1990 to manage the files, answer media and academic enquiries and allow access for citizens to their own files.

The commission has dealt with five million enquiries in the past 15 years and around 1.9 million Germans have applied to see their files. The interest remains high, with 10,000 file-viewing applications a month.

On Saturday, the Berliners who forced their way into the Stasi headquarters were invited to take a more orderly tour of the vast complex of buildings than their last visit, 15 years ago.

There's an enormous room with heavy revolving machines holding a large selection of the 32 million index cards.

Another room is filled with glass bell jars. Inside each jar is yellow cloth impregnated with the scent of political opponents and prisoners to aid their recapture with trained dogs. Adjacent to the vast file halls are smaller rooms filled with sacks of shredded and torn paper files.

The protesters recovered 16,000 bags of destroyed files in total and, since 1990 a 15-person team has worked full-time to piece together half a million pages, the contents of 250 sacks. At this rate, they will need another 400 years to complete the task, though a new computer scanning system is being tested to speed up the work.

The full-disclosure policy towards the Stasi files is expected to continue for another five years at least. Files of private citizens remain private but those of people deemed "historical figures" can be published.

The longest-running battle over a Stasi file has been fought by former Chancellor Helmut Kohl. He appears to have lost a four-year legal battle and his 7,000-page file is likely to be published soon, although he won the right to withhold what may be the most interesting bits.

East Berlin has vanished outside, but in the Stasi headquarters, everything remains eerily the same.

In the wood-panelled office on the second floor, it looks as though Erich Mielke, the Stasi chief, will arrive at any moment and sit down at his desk with the death mask of Lenin in the corner. In the adjacent secretary's office, a calendar hangs on the wall. The month: December 1989.