But what most attracted him to this area was the brothels that had sprung up like a rash once the Americans had taken over the city. Almost every taste was catered for by women – and men – who’d never ordinarily have contemplated prostitution. But desperation had forced hundreds of them onto the streets, and Friedrich found it was a perfect outlet for his appetites.

Eventually he rented a room near the Theresienwiese fairground, where the Oktoberfest was held every year. He’d become particularly attracted to a fifteen-year-old girl he’d bought from her Polish-German pimp for a whole night in return for a watch. He’d become rather friendly with the pimp, Emil, who seemed to specialise in younger girls and, it had to be said, boys – though this was something Friedrich preferred not to think about. Emil told him that he’d done what he called ‘specialist work’ in Poland during the war; as far as Friedrich could tell, this involved helping to run and then clear the Jewish ghettos.

Friedrich was impressed, and felt he could confide in Emil. He showed him his Gestapo badge and then told him he’d been almost single-handedly responsible for defeating the resistance throughout Europe. ‘In fact, so good was my reputation, they called me das Frettchen!’

It was true the girl – her name was Gisela – seemed to have been forced into prostitution, but Friedrich found himself thinking more and more about her, and when he took the room by the Theresienwiese, he decided to move her in, ignoring Emil’s protests. Things began to go wrong after that. Gisela turned out to be neither as obliging nor as grateful as Friedrich had assumed she’d be. Nor could she cook. She spent so much time hunched on the edge of the bed crying, jumping whenever he came near her, that she got on his nerves, and her behaviour didn’t change after he started beating her.

But far worse was to happen. He was drinking at a bar north of the station one afternoon when he found himself surrounded by Emil and two of his associates.

Where is Gisela?

Friedrich said he had no idea whatsoever, and pulled out his knife and threatened one of Emil’s associates. The brawl that followed was broken up by a squad of passing American military policemen. Friedrich, whose English was good, told them the men had attacked him because he’d criticised Hitler, and the policemen escorted him out of the bar.

But as they did so, Emil addressed them in equally good English. Far from being an anti-Nazi, did they realise the man they were taking away was a Nazi criminal?

The policemen stopped to listen, and rather than laughing it off, as he later realised he should have done, Friedrich shouted at Emil and called him a fucking liar, and said he’d tell them what he’d been up to.

‘If you don’t believe me’ said the Pole, standing very calmly at the bar, ‘he told me he’s a Gestapo officer known as das Frettchen. I’m sure you’ll find him somewhere in your files.’