I’d been sent on a HOLMES 2 familiarisation course three months earlier. At the time I’d been excited because I thought they might be preparing me for a role in major investigations, but now I realise they were grooming me for data entry work. It took me less than half an hour to find the Covent Garden investigation. People are often negligent about passwords, and Inspector Neblett had used his youngest daughter’s name and year of birth, which is just criminal. It also got me read-only access to the files we wanted.

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.