This week the authorities took the unusual step of publishing photos of the three men in an attempt to find their victim, who has never come forward to report the attack.

“The police have received a photograph of what we think is the same woman – we can only think this development has taken place as a result of our appeal to the public for help,” Michael Müller, Munich’s state prosecutor told The Local on Thursday.

But the woman has still not come forward, leaving a gap in the investigation – and the victim herself without the medical and psychological care she may need. The fear is that she may not remember what happened.

Müller said the men had been arrested after one of them was accused of a drugs-related offence. His mobile phone and computer were examined by police, who were horrified to find photographs of the woman being raped by two men.

Due to the poor quality of the photographs, police say she is between 14 and 28 years old, and between 1.50 and 1.65 metres tall with dark, shoulder-length, slightly wavy hair. The authorities have promised her absolute discretion should she come forward, but fear she may not remember the attack, or be too scared or upset to approach anyone.

It is thought she was drinking with the men during the Oktoberfest beer festival on October 7, 2007. She seems to have known one of them to a certain degree, and accompanied the trio back to his flat. There one of the three mixed knock-out drops into her drink and they attacked her.

“We do not need to have the victim in order to take the case to court, we have enough evidence for that. And we know what has happened,” Müller said.

But he admitted the authorities would like to have her testimony for sentencing – should it come to that – as a report on the effects on the victim makes an important impression on the court.

“Two of the men are being held in investigative custody while the third man is serving a three-year term on drugs charges,” he said.

The woman was wearing jeans and a black top on which ‘Liserl’ was written, and a wooden clothes peg was attached.

“It seems she may have been a student – the culprit she knew was a business (BWL) student at the Ludwig Maximilian University,” said Müller.

Police think she may live near the Prinzregentenstrasse, in Bogenhausen and could be called Lisa, Elisabeth, Alisa, Elisa or Lucie.