‘You tried to stall me at the underground rave,’ I said. ‘You didn’t want me going after him.’

‘And look what happened,’ said Zach.

‘So you do know him,’ said Lesley.

‘We may have crossed paths,’ said Zach. ‘Done a little business, socialised a bit.’

‘Who is he?’ asked Lesley.

‘His name’s Stephen,’ said Zach. ‘Any chance of a Mars bar?’

‘Surname?’ I asked.

‘Hot chocolate?’ asked Zach. ‘Nothing finishes off brawn like a hot chocolate.’

‘Surname?’

‘They don’t go in for surnames,’ said Zach.

I wanted to ask who ‘they’ were, but sometimes it’s better to let the interviewee think they’ve got one past you. So I asked where Stephen was from.

‘Peckham,’ said Zach.

We asked whereabouts in Peckham, exactly, but he said he didn’t know.

‘Do you know what he did with his gun?’ I asked.

‘What gun?’ asked Zach.

‘The gun he used to shoot at us,’ I said.

For a moment Zach was staring at us as if we were mad. Then he frowned.

‘Oh, that gun,’ he said. ‘You must have done something, because that gun’s purely for self-protection. I mean, I wouldn’t want you thinking that he just goes around shooting at anyone.’

‘Has he shown it to you?’

‘What?’

‘The gun,’ I said. ‘You ever seen it?’

Zach leant back in his seat and gave an airy wave. ‘Course,’ he said. ‘But not to hold or nothing.’

‘Do you know what kind of gun it was?’ asked Lesley.

‘It was a gun,’ said Zach making a pistol shape with his hand. ‘I don’t really know guns.’

‘Was it a revolver or a semiautomatic pistol?’ asked Lesley.

‘It was a Glock,’ said Zach. ‘Same as what the police use.’

‘I thought you didn’t know guns,’ I said.

‘That’s what Stephen said it was,’ said Zach. He turned to Lesley. ‘Any chance of that hot chocolate – I’m dying here.’

As a largely unarmed police force, the Met have some fairly serious views about the illegal possession of firearms. It tends to get a lot of attention from senior officers who are willing to devote substantial resources to the problem and usually ends in a visit from CO19, the Met’s firearms unit, whose unofficial motto is guns don’t kill people, we kill people with guns. Given that Zach must know how seriously we take it, the question had to be – what was so important that he was willing to implicate his friend Stephen in a firearms charge just to cover it up?

Especially given that having interviewed all the witnesses and searched Oxford Circus the Murder Team were pretty certain that Zach’s good friend ‘Stephen’ hadn’t been carrying one when he’d got off the train.

‘Hot chocolate was it?’ asked Lesley getting up.

‘Yes please,’ said Zach.