Ben Aaronovitch - Rivers of London

The old system couldn’t handle big data files, but because HOLMES 2 was only ten years behind the state of the art, detectives could now attach evidence photographs, document scans and even CCTV footage directly to what’s called a ‘nominal record’ file. It’s like YouTube for cops.

The Murder Team assigned to the William Skirmish murder had wasted no time grabbing the CCTV footage and seeing if they could get a look at the murderer. It was a big fat file and I went straight for it.

According to the report, the camera was mounted on the corner of James Street, looking west. It was low-quality, low-light footage updated at one frame per second. But despite the poor light it clearly showed William Skirmish walking from under the camera towards Henrietta Street.

‘There’s our suspect,’ said Lesley, pointing.

The screen showed another figure — the best you could say was probably male, probably in jeans and a leather jacket — walk past William Skirmish and vanish below the screen. According to the notes, this figure was being designated WITNESS A.

A third figure appeared, going away from the camera. I hit pause.

‘Doesn’t look like the same guy,’ said Lesley.

Definitely not. This man was wearing what looked like a Smurf hat and what l recognised as an Edwardian smoking jacket — don’t ask me why I know what an Edwardian smoking jacket looks like: let’s just say it has something to do with Doctor Who and leave it at that. Nicholas had said it was red, but the CCTV image was in black and white. I clicked back a couple of frames and then forward again. The first figure, WITNESS A, dropped out of shot one, two frames before the man in the smurf hat stepped into view.

‘That’s two seconds to get changed,’ said Lesley. ‘That’s not humanly possible.’

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.

‘Now you’re getting desperate,’ said Lesley.

‘Look at that chin and that nose,’ I said. ‘Nobody has a face like that.’

Lesley pointed to a notation attached to the image. ‘Looks like the Murder Team agree with you.’ There was a list of ‘actions’ associated with the evidence file, one of which was to check local costumiers, theatres and fancy-dress shops for masks. It had a very low priority.

‘Aha!’ I said. ‘So it might be the same person.’

‘Who can change their clothes in less than two seconds?’ asked Lesley. ‘Do me a favour.’

All the evidence files are linked, so I checked to see whether the Murder Team had managed to track WITNESS A as he left the crime scene. They hadn’t and, according to the action list, finding him had become a priority. I predicted a press conference and an appeal for witnesses. Police are particularly interested in talking to... would be the relevant phrase there.

Smurf Hat had been tracked all the way down New Row, exactly the route Nicholas had said he’d taken, but vanished off the surveillance grid in St Martin’s Lane. According to the ‘action’ list, half the Murder Team were currently scouring the surrounding streets for potential witnesses and clues.

‘No,’ said Lesley, reading my mind.

‘Nicholas …’

‘Nicholas the ghost,’ said Lesley.

‘Nicholas the corporeally challenged,’ I said, ‘was right about the murderer’s approach, the method of attack and cause of death. He was also right about the getaway route, and we don’t have a timeline where WITNESS A is visible at the same time as Smurf Hat.’

‘Smurf Hat?’

‘The murder suspect,’ I said. ‘I need to take this to the Murder Team.’

‘What are you going to say to the SIO?’ asked Lesley. ‘I met a ghost and he said that WITNESS A put on a mask and did it?’

‘No, I’m going to say that I was approached by a potential witness who, despite leaving the scene before I could get his name and address, generated potentially interesting leads that may further the successful outcome of the investigation.’

It made Lesley pause at least. ‘And you think that’ll get you out of the Case Progression Unit?’

‘It’s got to be worth a try,’ I said.

‘It’s not enough,’ said Lesley. ‘One: they’re already generating leads over WITNESS A, including the possibility that he was wearing a mask. Two: you could have got all that information from the video.’

‘They won’t know I had access to the video.’

‘Peter,’ said Lesley. ‘It shows someone’s head being knocked off. It’s going to be all over the internet by the end of the day, and that’s if it’s not on the ten o’clock news.’

‘Then I’ll generate more leads,’ I said.

‘You’re going to go looking for your ghost?’

‘Want to come?’

‘No,’ said Lesley. ‘Because tomorrow is the most important day of the rest of my career, and I am going to bed early with a cocoa and a copy of Blackstone’s Police Investigator’s Workbook.’