He went undercover to expose the unsavory journalistic practices of Germany's largest tabloid; he posed as "Ali" to document the life of a Turkish immigrant in Germany during the early 1980s.

If government documents from the former East Germany are to be believed, it appears investigative journalist Günter Wallraff took on another role as well: that of a Stasi spy.

The head of the authority that oversees the mountains of files seized from the headquarters of the East German secret police after the collapse of the GDR confirmed on Wednesday that Wallraff was listed in the files as an informant in the late 1960s. The confirmation ended years of speculation by various media on Wallraff's supposed Stasi connections.

"Based on our current knowledge," Marianne Birthler, the head of the authority, told the newspaper Die Welt, a "far-reaching exoneration" of Wallraff is no longer possible.

Die Welt first reported on the connection after getting hold of information on Wallraff (photo) contained on CD-ROMs recently released by the CIA. The so-called "Rosenwood" files were seized from Stasi offices during the confusing transition that followed the fall of the Berlin Wall. On July 1, the CIA removed the top secret designation on the files and sent them in the form of 381 CD-ROMs to Birthler's office.

The files allege that Wallraff, operating under the code name "Wagner," passed on documents from the Bundeswehr officer's training school and the chemical company Bayer AG to the Stasi while working for them from 1968 to the 1970s. The accusations, if proven, could be catastrophic for the respected leftist journalist and author's reputation.

Wallraff calls accusations baseless

Wallraff rose to fame when he worked under a false identity for Bild and left to write a tell-all book on the dirty newsgathering process of the mass-circulation daily in 1977. In the early 1980s, he "became" Ali, a Turkish immigrant who had come to work in Germany, and wrote a best-selling non-fiction book about his experiences.

The 60-year-old rigorously denied the charges on Wednesday.

"The new accusations are the old accusations, only that there are more index cards," said Wallraff, who lives in Cologne.

Most sensational story to come out of files

The story is likely to be the most sensational coming out of the files, say authorities. Many of the 200,000 people listed in the files were friends, colleagues or relatives of East German spies and only a small number actually worked as agents, Birthler said upon the files' release.

The Rosewood files are nevertheless believed to fill in a crucial gap in the extensive investigations of Stasi activities carried out by German authorities so far. Most Stasi documents seized from East German authorities only refer to spies by their code names.

For the first time the Rosewood files are expected to match real names to the code names, as Wallraff learned on Thursday.