I clicked forward. The man in the smurf hat produced his bat and stepped smartly up behind William Skirmish. The wind-up was between frames but the hit was clear. In the next frame Skirmish’s body was halfway to the ground and a little dark blob, which we decided must be the head, was just visible by the portico.

‘My God. He really did knock his head clean off,’ said Lesley.

Just as Nicholas had said he had.

‘Now that,’ I said, ‘is not humanly possible.’

‘You’ve seen a head come off before,’ said Lesley. ‘I was there, remember?’

‘That was a car accident,’ I said. ‘That’s two tons of metal, not a bat.’

‘Yeah,’ said Lesley, tapping the screen. ‘But there it is.’

‘There’s something wrong here.’

‘Apart from the horrible murder?’

I clicked back to where Smurf Hat entered the scene. ‘Can you see a bat?’

‘No,’ said Lesley. ‘Both his hands are visible. Maybe it’s on his back.’

I clicked forward. On the third frame the bat appeared in Smurf Hat’s hands as if by magic, but that could just have been an artefact of the one-second lag between frames. There was something else wrong with it too.

‘That’s much too big to be a baseball bat,’ I said.

The bat was at least two-thirds as long as the man who carried it. I clicked backwards and forwards a few times but I couldn’t work out where he was keeping it.

‘Maybe he likes to speak really softly,’ said Lesley.

‘Where do you even buy a bat that size?’

‘The Big Bat Shop?’ said Lesley. ‘Bats R Us?’

‘Let’s see if we can get a look at his face,’ I said.

‘Plus Size Bats,’ said Lesley.

I ignored her and clicked forward. The murder took less than three seconds, three frames: one the wind-up, two the blow and three the follow-through. The next frame caught Smurf Hat mid-turn, his face in three-quarter profile showing a jutting chin and a prominent hook nose. The frame after showed Smurf Hat walking back the way he’d come, slower than the approach, casual as far as I could tell from the stuttering image. The bat vanished two frames after the murder – again, I couldn’t see where it had gone.

I wondered if we could enhance the faces, and started looking for a graphic function I could use.

‘Idiot,’ said Lesley. ‘Murder Team will be all over that.’

She was right. Connected to the footage were links to enhanced pictures of William Skirmish, WITNESS A and the murdering gent in the smurf hat. Contrary to television, there’s an absolute limit to how good a closeup you can extrapolate from an old-fashioned bit of video tape. It doesn’t matter if it’s digital – if the information isn’t there, it isn’t there. Still, someone at the tech lab had done their best, and despite all the faces being blurry it was at least obvious that all three were different people.

‘He’s wearing a mask,’ I said.