Chapter 45

‘I have one last thing to show you,' Doyle said. ‘You too, Superintendent Nightingale.'

Nightingale frowned. ‘You've kept something back?'

Poe winced, but Doyle took it in her stride.

‘No, I was waiting for a confirmatory email. It has only just arrived. I saw no reason to burden you with my suspicions until then. I report facts, it's you who interprets those facts.'

‘And you have a new fact?' Nightingale asked.

‘Show slides twenty-three to twenty-eight on the monitor, please, Carlos.'

Doyle's assistant fiddled with the computer. The screen in the viewing room changed from the stun-gun marks to six close-ups of Cornelius's lower torso and upper thighs. They were just as heavily tattooed.

‘I understand an expert in religious iconography will go through the victim's tattoos with you,' Doyle said, ‘but I wanted to show you something that is more my field of expertise. Now, as you can see there are hundreds of tattoos on the victim's body, and because he's used every available bit of skin, it does appear they're a bit rough and ready.'

‘They're not?' Nightingale asked.

‘No. Most are exceptionally well done. The new ones are sharp with clear lines and the older ones haven't bled into the epidermis as much as you might expect. Probably because he's had a consistent body mass over the years.'

‘You said "most" were exceptionally well done,' Poe said. ‘I take it some weren't?'

‘No. Six alphanumeric strings stood out. I'll highlight them on the screen now.' Doyle walked over to her computer. She drew on a tablet with a stylus-type pen. Red circles appeared on the slides in the viewing area. ‘They're not easy to see so I've put them in a spreadsheet for you.' She tapped her tablet and a seventh slide appeared.

CC.58.R4.HI

SM.15.NP

AS.104X.GO

CSM.12.R2.CL

SB.47.R9.SG

SJE.77.PC

Now he knew what he was looking for, Poe could make out the corresponding letters and numbers on Cornelius Green's skin. There was something a bit off with them, something he couldn't quite put his finger on. Maybe a stylistic thing.

‘They're old tattoos,' Doyle said, ‘but I don't think they were done at the same time – the ink colour is inconsistent and I'm fairly sure different needles were used. At least two of the needles were blunt-judging by the scarred letters and numbers.'

‘Do you know what they mean?' Poe said.

‘I assumed they were Bible verses,' Doyle said. ‘But when I typed them into a reference site none got a hit. Your victim does have Bible verses tattooed on his torso, but these alphanumeric strings represent something else entirely.'

‘Any idea what?' Poe asked.

‘Even checking if they were Bible verses was stepping out of my remit and into yours.'

‘They aren't dark web URLs, they aren't lines of code, and I don't think they're passwords,' Bradshaw said. She was already on her computer. ‘Airline seat maps are alphanumeric, the seats are lettered but the rows are numbered, as are vehicle identification numbers.'

‘Can we try them?'

‘No point, Poe. VINs are seventeen characters long and airline seat maps follow a standard format. Seats start at A and go up to K on planes with four aisle seats and two lots of three window seats. And there's an I, and I isn't used as it can be mistaken for the number one. I'll try computer and mobile phone serial numbers, but I don't think that's what they are.'

‘Why not?'

Bradshaw shrugged. ‘What possible reason could there be? I suppose they could be numbered bank accounts, but I think that's unlikely.'

‘Why is that, Tilly?' Linus asked.

‘The numbers and letters don't work.'

‘They don't?' Linus leaned in to see what was on Bradshaw's screen.

‘Am I allowed to tell him, Poe?'

‘Go ahead, Tilly. He'll only snitch if you don't.'

Nightingale and Doyle smirked.

‘The alphanumeric strings don't work because if they were accounts from the same bank they would have the same number of letters and numbers. They don't. And if they were from different banks, we would not see R repeated the way it is. It's on three of the strings and always in the same place, four from the end. Statistically, that's so improbable I was able to discount it.'

Linus looked at Poe. ‘She's good,' he said.

Poe ignored him. ‘What else, Tilly?'

‘Usernames or passwords would be my next guess, although I doubt it. If something were so secret it had to be tattooed on his body, I would expect a more complex password chain. None of the alphanumeric strings contain special characters like an exclamation point or a hashtag. The strings also fit Benford's Law of naturally occurring collections of numbers, which suggests these are real-life sets of data.'

‘What's Benford's Law, Tilly?' Linus asked.

‘Benford's Law makes predictions about the frequency distribution of the first digit in large numerical data. If the first numbers were distributed uniformly, numbers one to nine would appear approximately eleven per cent of the time. But Benford's Law proves that number one appears first thirty per cent of the time, while number nine is first less than five per cent of the time. The number two is less likely to appear first than the number one, but more likely than three. This pattern continues all the way to nine. It's often used to detect fraud. Obviously, you and Poe are too dumb to understand the maths, so I won't bother explaining it.'

‘Aw,' Poe said.

‘So if Cornelius had chosen those numbers himself, he'd have selected more random numbers?' Linus said.

‘Exactly. But in these alphanumeric strings, the number one appears first fifty per cent of the time. They therefore comply with Benford's Law of real-life sets of data. That means they are real alphanumeric strings, not invented ones.'

‘I doubt it was anything like passwords anyway,' Poe said. ‘We've seen his room. There was nothing electronic in it. I probably know more about computers than Cornelius Green did.'

Bradshaw frowned. ‘Or at least the same.'

Nightingale hid a smile. Doyle openly guffawed.

‘Best guess as to what they are then?' Poe said, ignoring them.

‘I think this is a locally developed categorisation system, Poe,' Bradshaw said. ‘Without more data there is no way to decode it.'

‘Something to ponder,' Poe said. He faced Doyle. ‘They look homemade; was this what made them stand out?'

‘It wasn't,' Doyle replied. ‘Look again. And think about where they are on the body.'

He did. One was on Green's left thigh, two were on his right and the remaining three were on his lower torso, just above the groin area. All six were oblique rather than parallel. Poe frowned. He tilted his head and looked at them from a different angle. ‘They're upside down,' he said eventually.

‘Because?'

Poe paused, but only for a second. ‘Because he tattooed himself.'

Doyle winked. ‘I knew there was a reason I'm marrying you.' She faced Nightingale and said, ‘I took the liberty of sending the photographs to a forensic handwriting expert I know. It was his email I was waiting for. He confirmed that the formatting and the line and letter forms is the same on all six exemplars—'

‘Exemplars?'

‘What he calls samples. He confirmed that the same person wrote all six samples. That they are upside down, and on parts of the body Green could easily reach, supports our hypothesis.'

Poe nodded. He didn't doubt for a moment that Cornelius Green had tattooed himself and he could think of only one reason to do that. ‘He didn't want a record of them anywhere. Didn't want a tattooist remembering them. Tattoos like this stick in the memory.'

‘They must be there to remind him of something,' Nightingale said. ‘Something he couldn't risk forgetting.'

Poe considered that. Decided there was a more probable explanation. ‘Or they're a memento.'

‘A memento of what though?'

‘Nothing good,' he replied.