Police files revealing that Josef Fritzl had previous convictions and charges for rape emerged today as his victims came forward to speak about their ordeals.

Officials in Linz, Upper Austria, found files from 1967 showing that Fritzl was a known sex offender. His record contains a conviction for a rape and an attempt rape as well as an arrest for public exposure.

At least two victims have come forward so far. A nurse from Linz, who claims she was raped by Fritzl in October 1967, when she was 24, told a local paper: “As soon as I saw his picture on TV I knew: It was him. I recognised him by the eyes. I could not sleep the whole night after that.

The nurse, who is now 65, said that Fritzl had slipped through her ground-floor bedroom window while her husband was away on work.

"I felt someone pulling the bedclothes back and I thought it was my husband coming home," she said. "But then I felt this knife being pushed against my throat.

“He told me: ‘If you make a noise I'll kill you’. Then he raped me.“

Fritzl served only 18 months for the rape, allegedly because a judge considered he should be reunited with his wife and four children.

The files also show that he attempted to rape a 21-year-old in the same year, but the victim was able to escape.

The revelations will embarrass the officers in charge of the investigation in Amstetten, where Fritzl kept his daughter Elisabeth, locked up in a dungeon beneath his home for 24 years and fathered seven children with her.

Amstetten police and prosecutors had claimed that Fritzl had no criminal record. Even if he had been convicted, they said, Austrian law demanded that all records on sex offences are destroyed after ten years.

A spokesperson for the prosecutors handling the Fritzl case said: “We have requested to see these documents. We must examine them carefully as they obviously have great relevance for the case.”

A third victim, who was 20 at the time, also came forward after seeing Fritzl’s image in the news, to tell how he raped her in September 1967. But she did not report the case to the police because she did not want her friends and family to know about it.

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