Becker, who was arrested at her home last week in connection with the 1977 murder of the federal prosecutor general Siegfried Buback, featured in a documentary about the killing screened on public broadcast television on Wednesday night.

The film showed interview footage with a former intelligence agent who said Becker had given Germany's domestic intelligence agency, the Federal Office for the Protection of the Constitution (BfV), tip-offs leading to the subsequent arrest of two leading RAF figures, Brigitte Mohnhaupt and Christian Klar.

The man also said Becker had provided information about further assassinations planned by the group, sometimes referred to as the Baader-Meinhof gang. In return, she received money, which German media reports say amounted to some 100,000 deutschmarks (50,000 euros, $70,000).

It is not uncommon for the BfV to pay informants to provide information.

Wednesday's disclosure has led to calls from across the political spectrum for Interior Minister Wolfgang Schaeuble to release BfV files on Becker.

Right to view?

Wolfgang Bosbach, deputy head of the conservatives' (CDU) parliamentary group said a refusal to release the files led to suspicion that the state had something to hide.

"I wonder what state interest could be more important than getting to the bottom of a triple murder," Bosbach told the Neue Osnabruecker Zeitung.

In 2007, the interior ministry rejected an application to release the files, but the prosecutor general's office has now reapplied and the ministry is apparently thinking it over. But ministry spokesman Stefan Paris said the nature of the content meant it was unlikely it could be used in any legal proceedings.

"When the BfV works with informers who come forward to provide information on particular cases, such as Ms Becker did, it is always under a covenant of secrecy."

Bosbach has also called for clarity over the money Becker was allegedly paid for her insider knowledge. He said he could not understand how the state could fail to punish a lawbreaker and then pay her.

New evidence could lead to closure

The 57-year-old ex-Baader-Meinhof member was first arrested in 1977 after a shoot-out in which she seriously injured a policeman. She was sentenced to life imprisonment for attempted murder.

Investigators looked into Becker's involvement in the Buback slaying, but with a lack of evidence linking her to the case, they dropped it in 1980.

Three other RAF members were sentenced to long spells in jail for Buback's killing, but police have never established who fired the shots, as the terrorists refused to talk.

Becker, meanwhile, was released 12 years into her sentence and had been living in Berlin under an assumed name until police turned up new evidence implicating her in the triple murder. She was arrested again last week.

The authorities say they still don't believe she fired the shots that killed Buback and two others, but they say Becker's DNA, which was found on the envelopes of letters claiming responsibility for the crime, link her to it.

Michael Buback, the son of the murdered prosecutor general, however, believes Becker is the assassin the police have been looking for more than three decades.

In an interview with the Neue Westfaelische newspaper, he said he saw unbelievable mistakes and inadequacies in the futile efforts to find out who killed his father. "In my eyes, it seems likely that Verena Becker has been shielded by a protective hand," he said.

tkw/dpa/AP/Reuters
Editor: Nancy Isenson