‘So, I’ll scroll to after Justin White leaves, when something actually happens,’ he says, and Robin watches as the video fast-forwards. ‘I’m sorry to say,’ he continues, ‘but the camera angle isn’t great. It was positioned at the back of the van, facing forward, so you have quite a big black spot.’

‘But you see the murder?’ Craig asks him.

The techie hesitates. ‘See for yourself,’ he replies, stepping backwards.

The video plays. He’s right: the camera captures the monitors and equipment at the front of the van, but the entire back third is out of shot. The table, where Sharp was found, can only just be seen. But the quality is good and in colour: Finn and Sharp clear as they go about their work.

At first the film is boring. Both scientists sit in front of screens, watching an array of data. Occasionally, they talk; there’s no audio, but they seem to be smiling, their manner relaxed. The timestamp clicks round and Robin notices the camera start to shake slightly. It’s 01:10, the time the eye of the storm hit. The lights flicker; flashes of lightning burst outside the window. Both men seem happy – big grins on their faces, hands waving excitedly. At one point Sharp reaches over and enthusiastically hugs a smiling Finn.

Robin glances at Craig. She’s concentrating hard, her elbows on the desk, her chin resting on her hands. Robin knows this could be it. The moment that could free Finn – or put him away for good.

On screen, Finn has moved out of shot to the back of the van. He re-emerges a few minutes later, two plates with sandwiches in hand, and he passes one to Sharp. The two men sit back down in front of the monitors; the storm continues to thunder around them.

But then things start to change. Sharp stands up; his hands go to his throat. He seems to be choking, and Finn stands up next to him, thumping him twice on the back. Sharp’s shaking his head, and then he moves forward, ducking out of shot. Time ticks by. Only Finn can be seen, his face shocked, his eyes wide behind his glasses. He’s clearly panicking.

The two men have to crouch slightly in the small van; Robin remembers the cramped space, the feeling of claustrophobia that must have only worsened under stress. Robin watches as Finn’s hands flap; he walks to the monitors, then back again. He picks his mobile phone up, tries to make a call, throwing it down in frustration. Then he runs forward quickly, going out of shot.

‘Where have they gone?’ Robin snaps to the digital technician. ‘Why can’t we see them?’

The techie looks apologetic. ‘That’s what I meant, Sarge. The black spot.’

‘And there’s no other camera?’

‘No. There was a little Sony they used for filming earlier, but nothing else that captures this.’

‘Butler,’ Craig says. ‘Look.’