“Hang on,” said Pru. “Something’s happening.”

DAY TWENTY-NINE. 8.10 p.m.

The line of numbers at the bottom of the screen of the incident room television showed that it was 11.44. 11.44 and twenty-one seconds, twenty-two seconds, twenty-three seconds.

Coleridge still found it difficult to watch, even after numerous viewings. He had heard that the whole sequence was already available on the Internet and had been downloaded many tens of thousands of times. As long as he lived Coleridge did not believe he would understand how a single race of beings could include both Jesus Christ and the sort of people who would download a video of a young woman being murdered. He rather supposed that had been the Messiah’s point, but that didn’t make it any easier to understand or accept.

He, Hooper and Trish watched as, while Kelly sat naked and unsuspecting on the toilet, at the other end of the house, in the boys’ bedroom, the plastic flaps of the sweatbox moved. There was a sort of flurry of activity as a hidden figure swiftly gathered up one of the sheets that Peeping Tom had allowed for lavatory trips, spread it out to cover the entrance and on leaving the box enveloped his or her self in it. Try as they might, and using the best image-enhancement technology available, the police had been unable to gain any information whatsoever from that blurred bluish image. For a moment a hand was visible, but it was not possible to even tell if it was male or female, or even to say whether it wore a ring.

Then, carefully, covered from head to toe in the sheet, the hunched figure made its way out of the boys’ bedroom and into the glaring tube lighting of the living area. From there it went to the kitchen units, where it provided the police with another tantalizing glimpse of hand as it reached into one of the kitchen drawers and took out the largest kitchen knife available, a beautiful Sabatier. Then, as the murmuring and giggling that emanated from inside the sweatbox continued gently to waft into the microphones, the cloaked figure crossed the rest of the living room, went into the utility area and approached the toilet door.

DAY TWENTY-SEVEN. 11.44 p.m.

“Who the fuck is that, then?” said Geraldine, watching the sheeted figure emerge from the boys’ bedroom.

“Don’t know,” said Pru and Fogarty together.

“Someone’s having a laugh,” opined Fogarty. “Going to scare Kelly.”

Now the figure crossed to the kitchen units and picked up the knife from the kitchen drawer.

“That I do not like,” said Geraldine. “That is not funny.”

The figure was making its way towards the toilet now.

“They’re all far too pissed for this type of nonsense,” said Geraldine. “We need to make an announcement. Tell whichever silly cunt is in that sheet to stop fucking around and put that fucking knife back in the drawer before he gets us censored by the bleeding Standards Commission. Sam’s not here. You do it, Pru, quick, bang the intercom on.”

But there was no time.

The figure in the sheet suddenly threw open the toilet door and swept inside.

Kelly must have seen her killer’s face, but she was the only person who did. Every housemate knew the location of all the cameras intimately and whoever burst into that toilet knew that the only camera covering him was the one above the door. As he entered, he raised the sheet high above his head with both hands, one of which also held the knife. Kelly must have looked up in surprise, but it was not possible to see her expression in that final moment because the sheet was billowing above and behind the killer, cutting them both off from the view of the camera.

Now, as Geraldine and her editing team watched, the sheet seemed to fall downwards onto Kelly. This, it was to transpire, was the first plunge of the knife. The one that skewered Kelly’s neck.

In the monitoring box they still thought it was a wind-up. They had no reason to think anything else.

“What is that cunt doing?” Geraldine said, as the billowing sheet raised itself up again before plunging down once more.

DAY TWENTY-NINE. 8.30 p.m.

“I think he had been planning on making only one blow,” said Coleridge. “After all, he couldn’t afford to get any blood on him.”

“Tough call, that, if you happen to be knifing somebody.”

“Just one huge blow, straight into the brain. Instant death.”

“And no geyser of blood.”

“Exactly, but the girl must have moved her head and he hit the neck.”

“Fortunately for him not the jugular.”

“No, not the jugular. He got away without getting marked, just.”

“One lucky bastard.”

Coleridge was forced to agree: the killer had indeed been one lucky bastard.

“I still say it would take a man to deliver a blow like that, and a strong one,” Hooper continued.

“It doesn’t. We proved that,” said Trisha with a touch of impatience. She herself had spent an unpleasant afternoon at a local butcher’s shop plunging knives into pigs’ skulls.

“I know that a woman could have done it, but at what risk?” Hooper insisted. “If the knife had got stuck in the bone of the skull, for instance – that happened with the pigs, Trish, half the times you tried it. What’s more, the force required is huge, and there’s no guard on a kitchen knife. You were wearing gloves, but your hand slipped occasionally. What if hers had done? She’d have cut off her own fingers. Kelly would have grabbed the sheet. It would have been all up. The chances of a woman pulling off a blow like that are quite small.”

“Except for Sally,” Coleridge said. Big, beefy Sally. The Internet’s murderer of choice.

“Why on earth would Sally murder Kelly?” said Trish, a little too quickly.

“Why would any of them?” Coleridge answered. “The only thing we can say for sure is that any one of them could have done it. The killer was right-handed and so are all of the remaining housemates. However, I concede that it is more probable that one of the stronger ones did it. Probably a man.”

They all turned back to the screen. The figure had thrown open the door at 11.44 and twenty-nine seconds. The first blow had fallen two and a half seconds later, the next and final one two seconds after that. The killer had been inside the lavatory for considerably less than ten seconds in all.

“If it wasn’t all so damned clinical,” Coleridge observed, “I would have said that the attack was frenzied.”

The tape played on. The killer had clearly taken two sheets from the pile when he left the sweatbox, for now as he raised himself up from making the second blow he threw one over his victim. The other one continued to cover him as he left the toilet.

“And you talked to the cameraman on duty, constable?” Coleridge enquired.

“Yes, I did, sir,” Trish replied, “at length. His name is Larry Carlisle. He saw the figure in the sheet enter the lavatory and moments later he saw the figure emerge.” Trisha gathered up her case notes and quoted from the transcript of her interview with the cameraman…

“‘I saw the figure follow the victim into the toilet at approximately twenty to midnight. He re-emerged shortly thereafter and headed back across the living area towards the boys’ bedroom. I did not cover him with my camera as I had been instructed to continue to watch the toilet for Kelly in order to obtain more good nude footage. I remained there, watching the door, until the alarm was raised. I recall thinking that she was having a long time in the loo. I had only twenty minutes to go until my shift finished and I was beginning to think I’d have to leave her for the next bloke. Anyway, about four or five minutes after the figure in the sheet emerged, they all rushed down from the monitoring bunker, and you know the rest.’”