I shrugged. ‘It was just a hunch. I also told you that they would never dump a body on a traffic island in the middle of the West End.’ I nodded to the white tent. ‘And that’s exactly what they did. So I was wrong, too,’ I said.

I held out my hand to him and he went to shake it until he saw the blue latex gloves I was offering him.

‘Put these on and keep them on until you sign out at the perimeter. Don’t touch anything. Follow my instructions at all times.’

He signed in with the uniformed officer and put on the gloves and baggies. The officer and I held up the DO NOT CROSS tape as Professor Hitchens eased his great bulk under the tape. I had never seen a man so young who was so fabulously unfit.

‘Take your time, sir,’ the young uniform said, without irony.

Safely under the tape, Hitchens smoothed his corduroy suit and cleared his throat. We began walking towards the white tent and I found I had to slow my pace so that he could keep up.

‘We need to find the kill site,’ I said. ‘If the dump site has a ritualistic value for them, then possibly the kill site will have some significance too. The place where both the victims were hanged feels like it should ring some bells. There can’t be many late Victorian basements left in this town. If we find the kill site, it leads us to them. Any thoughts on where it could be?’

‘Where we are right now is London’s primary place of execution, as you so correctly observed.’

‘But they didn’t do it here, did they? They dump the bodies at Tyburn but they can’t hang them here. So where’s the next best thing?’

‘If ritual is that important to them, they’re spoilt for choice. It could be any one of a number of places of execution. Kennington Common, Shepherd’s Bush, Tower Hill, Charing Cross. Pirates were hanged at the execution dock at East Wapping. There were executions at Smithfield – although burning and boiling were preferred to hanging, especially during the sixteenth-century heresy trials. Charles I was executed in Whitehall. But Charles was beheaded – if we are talking specifically about hanging . . .’

‘What about Newgate?’ I said. ‘Didn’t they have hangings at Newgate after they stopped public executions at Tyburn?’

Professor Hitchens nodded his great oval head.

‘In many ways, Newgate would be their obvious choice. There was a gaol on that site for eight hundred years and after Tyburn’s gallows were abolished in 1783 public hangings continued at Newgate for almost another hundred years. Hangings were as popular as FA Cup Finals. Huge crowds would turn up to watch. The crush was apparently phenomenal. Often there would be a few dozen dead when the crowds went home for their supper. But Newgate Gaol was closed in 1902 and torn down in 1904.’