‘I can tell you about the unsub,’ the American said. ‘I can – I believe – also tell you something about Bob the Butcher. What I can’t tell you is that they are one and the same.’

Swire and Bush glanced at each other. And I saw just how desperately they both wanted Bob to be the same man – our killer.

‘Society struggles to understand the repeat serious offender,’ Dr Stephen continued. ‘The serial rapist and the serial killer. Often they are the same thing but at different stages on the road to madness.’

‘But there’s no sexual element to Bob’s crimes,’ Swire said.

‘My point is that the serial rapist and the serial killer tend to share the same basic characteristics. Because transgression is a way of life, they tend to be charming, manipulative, vain, ruthless, morally numb and devoid of even a shred of human empathy. The unsub will have a rich fantasy life – a fantasy life so rewarding that it will have come to have more substance than the real world. The unsub is likely to be a liar of near genius. As you know, serial killers often sail through lie detector tests. Trauma in his background is a given. Frequently, but not always, they come from backgrounds of mental and sexual abuse.’

Scarlet Bush perked up. ‘You think Bob the Butcher was the victim of child abuse?’

‘It’s possible. The rational mind struggles to understand the psychopathology of the irrational. These murders are an expression of the killer’s masculinity. As I said, these homicides are displays of honour, power and control. Their sole purpose is punishment – for some perceived wrong done against the killer himself or a third party. The killer almost certainly doesn’t know his victims. He is simply righting a wrong – or a series of wrongs.’

Scarlet Bush was jotting down notes.

‘So you’re saying that Bob the Butcher has a fragile masculinity?’ she said.

‘Not necessarily. But the unsub has a limited means of expressing his masculinity. He can’t do it, for example, in the business world. So he does it with violence. He does it with murder.’

‘What if I – I mean we – implied that there was, for example, a gay element to the crimes?’

Dr Stephen looked at her levelly. ‘I doubt you will endear yourself to him. Look, he’s seeking to gain control of a situation that is totally beyond his control. Unlike the overwhelming majority of murderers, he fully intends his victims to die. What’s unusual is that most homicides, as you know far better than me, are simply a by-product of extreme violence. Most murder victims are just unlucky.’

‘I’ll say,’ said Gane.

Dr Stephen had become good at ignoring him.

‘Medical help is delayed,’ he continued. ‘A vital organ is accidentally severed. A fatal injury is sustained when a head hits the pavement.’