‘There is a castle on the Rhine – Schloss Hochenstein. They called it the Institute of Developmental Psychology. The reality was that it was a euthanasia factory that also conducted radical psychological experiments. After the war, it became the record centre for the euthanasia programme. It has also been turned into a tourist attraction, though they don’t mention that particular element of the castle’s history,’ Wolf said, an ironic twist to his mouth. ‘Our reconciliation with our past only goes so far. We really don’t like to admit that we stood by and let our own children be slaughtered.’

‘No, I can see how that might be a bit hard for the national psyche to cope with,’ Tony said. ‘So, is it possible for me to gain access to these records?’

Wolf smiled, his thin lips spreading over yellowed teeth. ‘Normally, it would take time to obtain the necessary permissions. But I’m sure Petra can cut through all the red tape for you. She’s very good at getting her own way.’

Tony pulled a face. ‘So I’ve discovered.’ He pushed his half-drunk coffee away from him. ‘You’ve been a great help, Dr Wolf.’

The other man gave a self-deprecating shrug. ‘Any excuse to get away from campus for an hour.’

‘I know the feeling,’ Tony said, realizing as he spoke that he had already mentally left that life far behind him. ‘I’ll tell Petra she owes you a drink.’

Wolf snorted with laughter. ‘I won’t hold my breath. Good luck at the schloss.’

Luck was exactly what Tony felt he had on his side. The tide was slowly turning, allowing him to replace vague notions with real possibilities. It wasn’t a moment too soon. Given the escalation into overt sexuality that was evident in the Köln case, they needed to stop this killer before he lost even more of his self-control. Tony could easily imagine him turning into a spree killer, cutting a swathe through a university campus with a machine gun before turning his gun on himself. It was time to put a stop to it. He could feel his blood rising in anticipation. I’m coming for you, Geronimo, he thought as he walked out of the café into the clean spring day.