‘This should be simple. We sent a search warrant to the social network and received an IP audit within twenty-four hours. As I expected, Bob’s got an anonymiser. It’s a proxy server that acts as a privacy shield between the user and the rest of the digital world. Unless he’s a complete idiot – always a possibility – he was bound to have one. He might even have multiple anonymisers. I can usually work around them once I have the IP audit.’ He shook his head. ‘Usually. But Bob’s using some kind of enhanced security architecture. Onion routing, they call it. Tor or something similar, some beefed-up anonymity network that I’ve never seen. It routes data through multiple relays, encrypting and re-encrypting every time. It’s designed to make the web safe for whistleblowers – users reporting corporate or government corruption, and people living in dictatorships. Not serial killers.’

‘What are you telling us?’ Mallory said.

‘He’s gone deeper,’ Gane said. ‘Bob’s digital footprints are exactly like his fingerprints or glove prints.’ He shook his head. ‘Invisible.’

‘Turn it off,’ Whitestone said. ‘I’m sick of these idiots treating him like some kind of hero.’

The Bob the Butcher timeline had exploded with activity as the social network reacted to his message. The screen on Mallory’s wall unrolled a constant stream of fan mail, marriage proposals and slavish compliments. Gane stabbed a key and it was instantly gone from the screen, replaced with the still photograph of the seven boys at Potter’s Field.

‘I don’t know how they can make a hero of him,’ Whitestone said. ‘Someone who kills school friends.’

Mallory almost smiled.

‘But they don’t think he’s killing school friends,’ he said. ‘They think he’s killing the rich.’

After the morning briefing, Mallory and I walked from Savile Row to Hanover Square, where tall thin young women stood smoking in glamorous packs outside Vogue House.

We were expected at the law firm of Butterfield, Hunt and West, who had their offices on the north side of the great green expanse of Hanover Square. Salman Khan’s PA showed us into his office, then offered us coffee, tea or mineral water, sparkling or still. We were spoilt for choice. But before we could reply, Khan was rising up from behind his desk and telling us how to do our job.

‘But you must do more!’ Khan said, his upper-class English laced with just a trace of India. ‘This is simply not good enough! Two men murdered and no arrest? It’s appalling! I intend to take the matter up with Detective Chief Superintendent Swire, who is a friend of my father. Do I make myself absolutely clear?’

Mallory turned politely to the PA, who was still waiting in the doorway. ‘Tea, please, miss. A dash of milk and two sugars.’

He glanced at me.

‘Coffee, please,’ I said. ‘Short and black.’