‘This is how strangulation by hanging works,’ Elsa continued. ‘Once the noose is around your neck and there is nothing to support you, you are killed by your own body weight. Strangulation compresses the carotid arteries in the neck, shutting off the supply of blood to the brain and causing the brain to swell so much that it plugs the top of the spinal column. This causes a reaction known as the vagal reflex, which stops the heart. The compression of the neck closes the trachea and aborts the supply of oxygen to the lungs. So – no blood to the brain and no air to the lungs. Bad news. The victim passes out due to suffocation. And then he dies.’

‘How long does it take, Elsa?’ I asked.

‘It depends. But it is not a quick way to die. Strangulation by hanging takes at least five minutes, but no more than twenty.’

‘Do we have any defensive wounds?’

‘There are no defensive wounds on Mahmud Irani or Darren Donovan, although there are signs of advanced intravenous drug use on Mr Donovan.’

‘What does advanced mean?’ Dr Joe asked.

‘The veins of his arms had collapsed and he was shooting up between his toes,’ Elsa said. ‘But Hector Welles is the only one of them with extensive defensive wounds.’

I remembered Welles fighting for his life as the dark figures struggled to control him.

He knew what they had done to Mahmud Irani.

‘There are contusions and welts on Mr Welles’ arms where he was restrained,’ Elsa said. ‘Some facial bruising where he was punched or kicked.’ She smiled sadly at me. ‘But unfortunately no skin tissue under his fingernails, Max. Apart from his own.’

In the glare of the Iain West, the flayed neck of Hector Welles looked like the self-inflicted scars of some bizarre tribal ritual.

‘Hanging is of course a popular method of suicide. But Mr Irani and Mr Donovan both have burn marks on their wrists where their hands were secured behind their backs, precluding suicide. Mr Welles did not have his hands secured behind his back, making suicide a theoretical possibility – in fact, most suicide hangings look exactly like Mr Welles, as they change their mind when it is far too late and attempt to claw the noose from their neck. But the extent of his defensive wounds eliminates that.’

‘And three million hits on YouTube of the guy being hanged,’ Edie said.

Elsa Olsen looked at her sharply.

‘I’m looking at the medical evidence and not what’s trending on YouTube, Detective.’

‘Of course,’ Edie said.

Elsa nodded curtly. ‘And a suicide victim is unlikely to be cut down and dumped in the middle of Marble Arch. The dead don’t move themselves,’ she said. ‘In all three cases, the manner of death was murder.’

‘Anything you can give us about the knot?’ I said.