The wing commander needed a baby-sitter, so it was arranged for a WRAF girl, Rita Ellis, to do the duty. She was to wait outside her quarters, Block A, at RAF Halton, at 8 p.m., for the wing commander’s large white car which would pick her up. As she had never met him before, she was advised to be there on time.

Promptly at 8 p.m. that Saturday, November 11th, 1967, the car drew up and whisked her away. In the dark, Rita, 19, couldn’t see the colour of it, nor the full face of the driver. Five minutes later another car arrived. This was the white one, and it was, driven by the wing commander. He waited for a while, fuming at the baby-sitter’s non-appearance, and finally gave up, determined to put the WRAF girl on report on Monday morning.

He had no idea that Rita had already gone, in the wrong car. Or that she had gone to her death.

Next day her body was found in undergrowth near the RAF station’s Roman Catholic church. She was naked from the waist down and her knickers had been tightly tied round her neck, strangling her. Bruises on her face and body showed that she had been beaten as she tried to fight off her attacker, who had attempted to rape her.

The problem facing Scotland Yard was, who was the driver of the first car? It could have been any of the 2,000 RAF men or 670 civilians employed on the RAF station – or anyone else for that matter, as the base, near Wendover, Buckinghamshire, allowed free access to outside traffic.

The police were also left to ponder: did Rita’s killer know her exact timetable for that night, or did he arrive outside Block A and pick her up fortuitously?

At the inquest the coroner observed that the killer must be a man with a persistent psychosis who could strike again. He almost certainly did. On December 28th that same year a student nurse from Little Tring, three miles from RAF Halton, was dragged into a field, beaten about the head, raped and left unconscious by a man she described as between 25 and 30, with a long, thin face and “puffy” slit eyes.

In the following month a 15-year-old girl in a nearby village was accosted by a man whose description matched the one given by the student nurse.