‘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.
‘What’s happened?’
He doesn’t answer.
A shiver of alarm swarms across my shoulder blades. Something is wrong. I hear Julianne’s name mentioned. I yell above the voices.
‘Tell me what’s happened.’
Faces turn. They’re looking at me, staring. Nobody answers. The soft wetness of my own breathing is louder than the ringing phones and shuffling feet.
‘Where’s Julianne? What’s happened?’
‘One of our officers has been seriously injured,’ says Veronica Cray, hesitating for a moment before continuing. ‘He was guarding your wife’s hotel room.’
‘Guarding her.’
‘Yes.’
‘Where is she?’
‘We’re searching the hotel and surrounding streets.’
‘She’s missing?’
‘Yes.’ She pauses. ‘There are cameras in the foyer and outside on the street. We’re retrieving the footage…’
I’m watching her mouth move but not hearing the words. Julianne’s hotel was near Temple Circus. According to Oliver Rabb, that’s the same area that Gideon phoned me from at 3.15 a.m. He must have been watching her.
Everything has changed again, shivering and shifting, detaching from my conception like a fragment of sanity jarred loose in the night. I close my eyes for a moment and try to picture myself free, but instead witness my own helplessness. I curse myself. I curse Mr Parkinson. I curse Gideon Tyler. I will not let him take my family from me. I will not let him destroy me.
The morning briefing is standing room only. Detectives are perched on the edge of desks, leaning on pillars and looking over shoulders. The sense of urgency has been augmented by disbelief and shock. One of their own is in hospital with a collapsed windpipe and possible brain damage from oxygen deprivation.
Veronica Cray stands on a chair to be seen. She outlines the operation- a mobile intercept involving two- dozen unmarked vehicles and helicopters from the police air wing.
‘Based on previous calls, Gideon will use a mobile and keep moving. Phase one is protection. Phase two is to trace the call. Phase three is contact with the target. Phase four is the arrest.’
She goes on to explain the communications. A radio silence will operate between the cars. A codeword and number will identify each unit. The phrase, ‘Pedestrian knocked down’ is the signal to move, accompanied by a street and cross street.
A hand goes up. ‘Is he armed, boss?’
Cray glances at the sheet in her hand. ‘The detective guarding Mrs O’Loughlin was carrying a regulation sidearm. The pistol is now missing.’
The resolve in the room seems to stiffen. Monk wants to know why it’s an intercept and arrest. Why not follow Tyler?
‘We can’t take the risk of losing him.’
‘What about the hostages?’
‘We’ll find them once we have Tyler.’
The DI makes it sound like the logical course of action, but I suspect her hand is being forced. The military want Tyler in custody and know exactly how to apply pressure. Nobody questions her decision. Copies of Tyler’s photograph are passed from hand to hand. Detectives pause to look at the image. I know what they’re wondering. They want to know if it’s obvious, if it’s visible, if someone like Tyler wears his depravity like a badge or a tattoo. They want to imagine they can recognise wickedness and immorality in another person, can see it in their eyes or read it on their faces. It’s not true. The world is full of broken people and most of their cracks are on the inside.
From across the incident room comes the sound of a toppling chair and the clatter of a wastepaper bin being kicked through the air. Ruiz comes raging between desks, stabbing his finger at Veronica Cray.
‘How many officers were guarding her?’
DI Cray gives him an icy stare. ‘I would advise you to calm down and remember who you’re talking to.’
‘How many?’
She matches his anger. ‘I will not have this discussion here.’
Around me, the detectives are transfixed, bracing for the clash of egos. It’s like watching two wildebeest
