Reid reached across and double-clicked on the icon that appeared. Windows Media Player sprung to life and after a few seconds of solid black, a street scene snapped into view. The image was far from sharp, but the wide-angled fish-eye lens showed both sides of the street peeling away from the road, perspective slightly distorted. The time in the corner read just before 3 p.m. According to the report Anderson had filed, the shots they were watching were two hours before they had charged into the building. It was like watching stop-motion animation. Cars were there on one shot, gone the next. The few people he saw advanced along the street in leaps of twenty feet. Reid dragged the cursor across the scroll bar, and the images flickered, strobe-like, as he travelled through time.

The clock read 17.05. A black Mercedes appeared at the top of the screen, taking three frames to pull up outside Taylor Fisheries. Two men exited the car. There was no mistaking Bolton. The only place he would blend in would be the gorilla cage at the zoo. Porter noted the second man getting out of the passenger side: Owen Carter.

The two men disappeared inside and the car vanished soon after. The stop-start motion made for a painful viewing experience, and Porter motioned for Reid to skip forward to the action. He fixed his eyes on the window, waiting for the explosion of glass and splintered frame.

When it came, it was like a magic trick. Carter hovering in the air one second, on the ground the next. Porter saw figures appear from the far right corner, advancing quickly towards the building. He swallowed hard as he recognised Simmons, keeping pace with Gibson; he leant forward, grabbing the mouse to pause it, as if that would stop what was to come.

‘Wait,’ said Reid. ‘Go back a bit. Nope, not that far … Here, let me.’

Porter surrendered control of the mouse. Reid dragged the marker on the progress bar back a few millimetres, the image frozen with Carter on the ground.

‘There.’ He stabbed a finger towards the gaping hole that used to be the window. ‘Look there.’

Porter stared at the darkness inside the window frame, at the amorphous blob, more grey than black, centred within it, but he could no more identify the person than he could stop Simmons’s charge. He knew it was Bolton, but knowing it and proving it were different things entirely. They could prove Bolton went into the building, now, though, that was something, and maybe even enough to get Campbell’s sign-off to bring him back in.

Reid’s finger twitched again, the picture advanced to the next frame, and Porter froze, eyebrows arching upwards. The figure was leaning forward, looking out onto the road. He hadn’t noticed it on the first run-through; his attention had been fixed on Carter. It leant into the daylight, taking on shape, the unmistakable shape of James Bolton.