Any sign of weakness is preyed upon. He can recognise a flagging heart, distinguish inner strength from a charade and find the fault lines in a psyche. We’re not so different, he and I, but we aspire to different ends. He tears minds apart. I try to repair them.
Oliver and Lieutenant William Greene are at work in their goldfish bowl-like office, leaning over laptops and comparing data. They make an odd couple. The lieutenant reminds of one of those wind-up toy soldiers with a stiff legged gait and a fixed look on his face. The only thing missing is a large key rotating between his shoulder blades.
A large map takes up the entire wall, dotted with coloured pins and crisscrossed with lines that join them, forming series of overlapping triangles. The last call from Gideon Tyler originated from Temple Circus in the centre of Bristol. Police are studying CCTV footage from four cameras to see if it can link the call to a vehicle.
The mobile phone hidden in Charlie’s bedroom went missing from a boating supply shop in Princes Wharf on Friday. The handset Gideon used to make the call has been traced to a phone shop in Chiswick, London. The name and address of the buyer were those of a student living in a shared house in Bristol. A gas bill and credit card receipt (both stolen) were used as proof of identity.
I study the map, trying to acquire the nomenclature to read the red, green and black pins. It’s like learning a new alphabet.
‘It’s not complete,’ says the lieutenant, ‘but we’ve managed to trace most of the calls.’
He explains that the coloured pins represent phone calls made by Gideon Tyler and the nearest transmitting tower to each signal. The duration of each call has been logged, along with the time and signal strengths. Gideon hasn’t used the same handset more than half a dozen times and he never calls from the same location. In almost every case the handset was turned on only moments before he made the call and turned off immediately afterwards.
Oliver talks me through the chronology, starting with Christine Wheeler’s disappearance. The signals can place Gideon Tyler in Leigh Woods and near the Clifton Suspension Bridge when she jumped. He was also within a hundred metres of Sylvia Furness when her body was handcuffed to the tree and in Victoria Park in Bath when Maureen Bracken aimed a pistol at my chest.
I study the map again, feeling the landscape rise up from the paper, becoming solid. Amid the predominantly red, green and blue pins, a lone white pin stands out.
‘What does that one mean?’ I ask.
‘It’s an anomaly,’ explains Oliver.
‘What sort of anomaly?’
‘It wasn’t a phone call. The handset pinged for a tower and then went dead.’
‘Why?’
‘Perhaps he turned the phone on and then changed his mind.’
‘Or it could be a mistake,’ suggests the lieutenant.
Oliver looks at him irritably. ‘In my experience mistakes happen for a reason.’
My fingertips brush the pinheads as reading a document in Braille. They come to rest on the white pin.
‘How long was the phone turned on for?’
‘No more than fourteen seconds,’ says Oliver. ‘The digital signal is transmitted every seven seconds. It was picked up twice by the tower we’ve marked. The white pin is the location of the nearest tower.’
Errors and anomalies are the bane of behavioural scientists and cognitive psychologists. We look for patterns in the data to support our theories, which is why anomalies are so damaging and why, if we’re very lucky, a theory will hold together just long enough for a better one to come along.
Gideon has been so careful about not leaving footprints, digital or otherwise. He has made precious few mistakes that we know of. Patrick’s sister ordered a pizza with Christine Wheeler’s mobilethat’s the only mistake I can remember. Perhaps this was another one.
‘Can you trace it?’ I ask.
Oliver has pushed his glasses up his nose again and tilted his head back to bring my whole face into focus.
‘I suppose the signal may have been picked up by other towers.’
The lieutenant looks at him incredulously. ‘The phone was only turned on for fourteen seconds. That’s like trying to find a fart in a windstorm.’
Oliver raises his eyebrows. ‘What a colourful analogy! Am I to assume that the army isn’t up to the job?’
Lieutenant Greene knows that he’s being challenged, which he finds vaguely insulting because he clearly thinks Oliver is a chin-less, pale, limp-wristed boffin who couldn’t find his arse with both hands.
I take some of the tension out of the moment. ‘Explain to me what’s going to happen when Tyler calls again.’
Oliver explains the technology and the benefit of satellite tracking. The lieutenant seems uncomfortable discussing the subject, as though military secrets are being revealed.
‘How quickly can you trace Tyler’s call?’
‘That depends,’ says Oliver. ‘Signal strengths vary from place to place in a mobile network. There are dead spots created by buildings or terrain. These can be mapped and we can make allowances, but this isn’t foolproof. Ideally we need signals from at least three different towers. Radio waves travel at a known rate, so we can work out how far they’ve travelled.’
‘What if you get a signal from only one tower?’
‘This gives us DOA- direction of arrival- and a rough idea of the distance. Each kilometre delays the signal by three microseconds.’
Oliver takes a pen from behind his ear and begins drawing towers and intersecting lines on a piece of paper.
‘The problem with a DOA reading is the signal could be bouncing off a building or an obstacle. We can’t always trust them. Signals from three base stations give us enough information to triangulate a location as long as the clocks at each of the base stations are synchronised exactly.’
‘We’re talking microseconds,’ adds Oliver. ‘By calculating the difference in the arrival times it’s possible to locate a handset using hyperbolas and linear algebra. However, the caller must be stationary. If Tyler is in a car or on a bus or a train it won’t work. Even if he walks into a building there will be a change in signal strength.’
‘How long does he have to stay in one place?’
Oliver and the lieutenant look at each other. ‘Five, maybe ten minutes,’ says Oliver.
‘What if he uses a landline- something fixed?’
The lieutenant shakes his head. ‘He won’t risk it.’
‘What if we make him?’
He raises his eyebrows. ‘How you plan to do that?’
‘How easy is it to shut down mobile phone towers?’
‘The phone servers would never agree. They’d lose too much money,’ says Lieutenant Greene.
‘It won’t be for long. Ten minutes maybe.’
‘That’s going to stop thousands of phone calls. Customers are going to be very pissed off.’
Oliver seems more open to the idea. He looks at the map on the wall. Most of Gideon’s calls have come from central Bristol where most of the phone towers are concentrated. More servers would have to co-operate. He thinks out loud. ‘A limited geographical area, fifteen towers maybe.’ His interest is sparked. ‘I don’t know if it’s ever been done.’
‘But it’s possible.’
‘Feasible.’
He turns and sits at a laptop, his fingers dancing on the keyboard, as his glasses slip further and further down his nose. Oliver, I sense, is happier in the company of computers. He can reason with them. He can understand how they process information. A computer doesn’t care whether or not he brushes his teeth or cuts his toenails in the bath or wears socks to bed. Some would say this is true love.
64
There are shouts and people running. Veronica Cray is yelling orders above the commotion and police officers are heading for the stairs and the lift. I can’t hear what she’s saying. A detective almost knocks me over and mumbles an apology as he picks up my walking stick.