‘Because the rope – or belt, or bed sheet, or wire, or whatever it is – angles towards the knot. See how deep it is? He was strangled by his own body weight. The rope compresses the carotid arteries, turns off the supply of blood to the brain. In judicial hangings, they used to snap the second cervical vertebra – the hangman’s fracture, they call it. More humane. These guys didn’t bother with any of that. They just strung him up. But hangings always look like this – the angled strangulation mark. What’s unusual about this one is that it’s not a suicide.’ She stood up. ‘Every hanging I ever saw until tonight – and I’ve had my share – was either deliberate or accidental suicide.’

‘Accidental suicide?’

‘Autoerotic asphyxia. You know. Sex games that kill you.’

‘Oh.’

‘It tends to be a male pastime, like doing DIY or watching cricket. Women seem less keen on autoerotic asphyxia. But strangulation apparently heightens the intensity of orgasm. And what could possibly go wrong?’ She nodded at the body. ‘What’s unique about Mahmud Irani is that his hanging was not for the purposes of masturbation or ending his life. It was murder. Who uses hanging to murder someone?’

I thought about it.

‘Somebody who wants revenge?’

‘No – somebody who wants justice.’ Her eyes scanned the park. ‘This is not the killing ground, is it? He didn’t die here.’

I thought of the white-tiled room where no light seemed to shine. And I thought of the underground car parks that were in this area, not just by Hyde Park but also under the grand hotels and the fancy car dealerships of Park Lane. None of them, as far as I knew, looked even remotely like the room in the film, which looked like somewhere that should have been torn down a hundred years ago.

‘So they chose to move him from the kill site to the dumping ground,’ I said. ‘Why would they do that?’

‘Makes it harder for us,’ Whitestone said. ‘Now we can’t run forensics on the kill site.’

‘Yes, but it makes it more dangerous for them. Why risk someone seeing them dump the body? Why not leave him where they’d strung him up?’

Whitestone thought about it.

‘Because they wanted us to find him,’ she said.

We watched the Specialist Search Team inching their way across Hyde Park on their hands and knees. In the distance, a German Shepherd from the Dog Support Unit began to bark.

‘What I could really use is the rope they did it with,’ Whitestone said, more to herself than me. ‘Ropes can speak volumes. The kind of rope. The kind of knot.’