'Shit,' Harry said. 'Are you absolutely sure?'

Weber gave a tired smile. 'The fingerprint on the bottle is so good that if we had had it on our files, the computer would have found a match. Of course, we could search manually to be one hundred and ten per cent sure, but it would take weeks and we wouldn't find anything, anyway. It's definite.'

'Sorry,' Harry said. 'I was just so sure we had him. I reckoned the chances of a guy like him never having been arrested for anything were microscopic.'

'The fact that we don't have him in our archives just means we have to look elsewhere. But now at least we have tangible evidence. This fingerprint and the fibres from Kirkeveien. If you can find the man, we have conclusive proof. Helgesen!'

A young man passing by pulled up smartly.

'I was given this cap from the Akerselva in an unsealed bag,' Weber grumbled. 'This isn't a pigsty we're running. Have you got that?'

Helgesen nodded and sent Harry a knowing look.

'You'll have to take it like a man,' Weber said, turning to Harry again. 'At least you didn't have to put up with what Ivarsson went through today.'

'Ivarsson?'

'Haven't you heard what happened in the Culvert today?'

Harry shook his head and Weber chuckled and rubbed his hands. 'In that case, I'll tell you a good story to help you on your way, Hole.'

***

Weber's presentation was a lot like the police reports he wrote. Brief, rough-hewn sentences sketching out the action taken without any florid descriptions of feelings, tone of voice or facial expression. Harry had no problem filling in the gaps though. He could visualise PAS Rune Ivarsson and Weber going into one of the visitors' rooms in A-Wing and could hear the door being locked behind them. Both rooms were next to the reception desk and kitted out for families. Inmates could enjoy a few moments of peace with their nearest and dearest in a room which someone had even tried to make cosy-basic furnishings, plastic flowers and a couple of pale watercolours on the wall.

Raskol was standing when the two of them arrived. He had a thick book under his arm, and on the low table in front of them there was a chessboard with the pieces set up and ready. He didn't say a word, just beheld them with his pained brown eyes. He was wearing a white coat-like shirt hanging almost down to his knees. Ivarsson was ill at ease and brusquely told the tall, thin gypsy to take a seat. Raskol obeyed the order with a slight smile.

Ivarsson had taken Weber with him instead of the younger officers in the investigation team because he thought that the old fox would be able to help Ivarsson 'size Raskol up', as he put it. Weber placed a chair against the door and took out a notebook while Ivarsson sat face to face with the infamous prisoner.

'Please, Politiavdelingssjef Ivarsson,' Raskol said, displaying an open palm to invite the policeman to start the game.

'We have come here to gather information, not to play games,' Ivarsson said and placed five photographs of the robbery in Bogstadveien beside each other across the table. 'We would like to know who this is.'

Raskol picked up the photos one after the other and studied them with loud 'hm's.

'May I borrow a pen?' he asked, after looking at all of them.

Weber and Ivarsson exchanged glances.

'Take mine,' Weber said, passing him a fountain pen.

'I prefer the usual kind,' Raskol said without taking his eyes off Ivarsson.

The PAS shrugged, took out a biro from his inside pocket and gave it to him.

'First of all, I would like to explain the principle behind dye cartridges,' Raskol said, beginning to unscrew Ivarsson's white pen, which happened to bear the Den norske Bank logo. 'As you know, bank employees always add a dye cartridge to the money in case they are raided. The cartridge is attached to money dispensers in an ATM. Some cartridges are connected to a transmitter and are activated by movement, being put in a bag for example. Others are activated when they pass a portal which may be secured above the main door of a bank. The cartridge may have a micro-transmitter connected to a receiver which triggers an explosion when it is a certain distance from the receiver, say, a hundred metres. Others explode after an inbuilt time delay post-activation. The cartridge itself can have all sorts of formats, but it has to be so small that it can be hidden between notes. Some are this small.' Raskol held his thumb and forefinger two centimetres apart. 'The explosion is not dangerous to the robber; the problem is the dye, the ink.'

He held up the ink cartridge from the biro.

'My grandfather was an ink maker. He taught me that in the old days they used gum arabic to make iron gallus ink. The gum comes from the acacia tree and is called Arabia's tears because it trickles out in yellowish drops this size.'

He made a circle with his thumb and forefinger, about the size of a walnut.

'The point about the gum is that it thickens and reduces the surface tension of ink. And it keeps iron salts liquid. You also need a solvent. Long ago rainwater or white wine were recommended. Or vinegar. My grandfather said you should add vinegar to the ink when you were writing to an enemy and wine when you were writing to a friend.'

Ivarsson cleared his throat, but Raskol continued regardless.

'At first, the ink is invisible. It becomes visible when put on paper. In the dye cartridge there are red particles which perform a chemical reaction when they come into contact with the paper of banknotes and this makes it impossible to remove. The money will be forever marked as robbery money.'

'I know how a dye cartridge works,' Ivarsson said. 'I would rather know-'

'Patience, dear Politiavdelingssjef. The fascinating thing about this technology is that it is extremely simple. So simple that I could make a dye cartridge myself, put it wherever I liked and make it explode at a certain distance from the receiver. All the equipment required would fit into a lunch box.'

Weber had stopped taking notes.

'But the principle of the cartridge is not the technology, PAS Ivarsson. The principle is incrimination.' Raskol's face lit up into a huge smile. 'The ink also attaches itself to the clothes and skin of the robber. And the ink is so strong that once it is on your hands you will never be able to wash it off. Pontius Pilate and Judas, right? Blood on his hands. Blood money. The agony of the arbiter. The punishment of the informer.'

Raskol dropped the ink cartridge on the floor behind the table and while he bent to pick it up, Ivarsson signalled to Weber that he wanted the notebook.

'I would like you to write the name of the person in the photos,' Ivarsson said and put the pad on the table. 'As I said, we are not here to play games.'

'Not to play games, no,' Raskol said, slowly screwing the pen together. 'I promised I would give you the name of the man who took the money, didn't I?'

'That was the agreement, yes.' Ivarsson said. He leaned over as Raskol started to write.

'We Xoraxans know what an agreement is,' he said. 'I'm not just writing his name, but also the prostitute he uses regularly and the man he contacted to shatter the knee of a young man who recently broke his daughter's heart. The person in question refused the job by the way.'

'Ah…excellent.' Ivarsson turned quickly to Weber and gave an excited grin.

'Here.' Raskol handed the pad and pen to Ivarsson, who hurriedly read the note.

The elated smile died. 'But…' he stammered. 'Helge Klementsen. He's the branch manager.' A light of illumination revealed itself to him. 'Is he involved?'

'Very much so,' Raskol said. 'He took the money, didn't he?'

'And put it in the robber's holdall,' came Weber's deep growl from the door.