Perfect Prey. Helen Fields

He leaves the central library room from the staff area and walks towards the front doors. We’re assuming that was him intending to leave for the night.’

      ‘Run it back a bit,’ Callanach said. The footage reversed for a couple of seconds at high speed and Callanach hit the space bar to stop it. ‘Play it from here.’

      Michael Swan could be seen from the camera at the rear of the main room walking towards the staff area at the right-hand side of frame. He paused once, turned his head. Walked out of frame, then came straight back, walking out towards the main doors. The latter part was the shot they’d watched initially.

      ‘He’s not carrying anything,’ Salter said.

      ‘Actually, if you look carefully you’ll see he has his keys in his hand when he walks back across. That’s what makes it obvious that he’s about to leave,’ the CSI said, sighing as she spoke.

      ‘How often do you leave work after a whole day with nothing in your hands?’ Salter responded.

      ‘It’s summer,’ the technician replied, brushing hair out of her eyes and adopting a tone of voice midway between stroppy and defensive. ‘He hardly needs a coat. I don’t see how this is evidentially important.’

      Salter clearly had more to say. She looked at Callanach before continuing. It wasn’t like her to get involved in an argument, but he could see she wasn’t done yet.

      ‘Have you had another member of the library staff show you Mr Swan’s personal effects?’ Salter asked, ignoring the challenge and following her own line of thought.

      ‘Of course. There’s the usual work paraphernalia, mugs, pens, notes, a book he was in the middle of reading. Some other random personal correspondence. We’ve followed procedure. Everything’s been bagged and tagged.’

      ‘Could we see it, please?’ Salter asked. The tech called a uniformed officer over, who promptly disappeared then returned with a large clear plastic bag containing several other smaller plastic bags, each containing a single item. Every bag had a label with a unique reference number, time, date and location on it. Callanach and Salter looked through each one.

      ‘Here,’ Salter said, holding up one particular bag with a thick piece of card, bearing gold leaf edging and italic printing. Michael Swan’s name was written in pride of place. Salter read it out. ‘“You are hereby invited to attend Edinburgh City’s Community Achievement Awards.” This was being held the morning after his death. And it says very clearly that the invitation must be produced at the door for entry.’

      The tech officer had stopped looking stroppy and was fiddling with her laptop instead.

      ‘So he forgot it,’ she snapped.

      ‘I don’t think so,’ Salter addressed Callanach directly. ‘His wife told us he’d been looking forward to that. It would have been on his mind all day. I don’t believe he was ready to leave when he went towards the door.’

      Salter rewound the CCTV footage again and hit play.

      ‘You see here, sir,’ she said, pointing at Michael Swan’s face as he turned mid-walk. ‘He hears something or is distracted by something. We know then he picks up his keys and goes towards the front door. I reckon he opened the door for someone else to come in. Not for him to get out. That’s why he hadn’t picked up the invitation yet.’

      Callanach watched the footage one more time, then looked back at Salter.

      ‘Remind me again why you missed the last round of sergeant exams, DC Salter,’ he said.

      ‘I was on honeymoon, sir,’ Salter said.

      ‘Make sure you’re available to take them next time. That’s an order,’ Callanach said.

      ‘I might be too busy in six months’ time,’ Salter said. ‘I could get talent-spotted by a Hollywood agency or appear on Masterchef and end up opening my own restaurant.’

      ‘I doubt that,’ Callanach said. ‘I’ve tasted your toasted sandwiches. Seriously. You’d have passed the exams at the last sitting. Don’t let it wait.’

      ‘Detective Inspector,’ Ailsa Lambert shouted from the doorway. ‘You only have me for another few minutes. There are reports of an incident across the city. My team will hold the scene for me briefly, but it’s now or never. I’ve a full day ahead.’

      They walked down into the basement, hastily donning white crime scene overalls, shoe covers and gloves. The scene was entirely different to the snapshot Callanach had of it from when he’d fallen. The area was now lit from all angles. Michael Swan’s body had, of course, been taken down but he was still suspended there in Callanach’s mind.

      ‘Two questions,’Callanach said. ‘How did the killer get Mr Swan to come down here, and how did they get him into position hanging from the overhead metal beams?’

      ‘If he let the killer into the building voluntarily,’ Salter said, ‘it must either have been someone he recognised or someone who seemed non-threatening.’

      ‘Okay, assuming either case, once in the building they persuaded him to open the basement and come inside.’

      ‘Easy enough if they were armed,’ Ailsa noted, pulling a thick wad of A4 photos from a folder. ‘Showing a knife or a gun would have the desired effect. Getting the man seven feet into the air makes less sense. The killer would have had to put down their weapon. No way of tying these knots without two hands.’ Ailsa paused to point out close-ups of the knots. Both were tied in the same way, one binding the hands, one binding the ankles, then another rope had been passed through the ankle knot, through the hand knot and looped around his neck.

      ‘What damage did the rope around his neck do?’ Callanach asked.

      ‘Very little in real terms, and it certainly wasn’t strangulation that killed him. The rope would have been useful to keep him still whilst his face was skinned. Of course, he’d have been on his back whilst that was being done. Other than that, once he was hoisted up to the ceiling, it simply held his head in place until he was found. There’s virtually no internal damage to the neck or throat area, only external bruising and chafing of the skin.’

      Callanach moved to stand in the area where he’d fallen, directly below the space that Michael Swan’s face had filled.

      ‘So he stood still whilst his hands and feet were tied. The killer at that point holding no weapon. Mr Swan is then restrained by the additional rope fed from ankles to neck, and is laid on his back and skinned whilst still conscious.’

      ‘No drugs in his system, no blow to the head. I’m as sure as I can be that he was conscious when it started. I would guess he blacked out from shock and pain at some point, but he might well have come round again prior to blood loss stopping his heart and starving his brain of oxygen.’

      ‘So he must have been hoisted up,’ Callanach said.

      Ailsa handed him a different photograph. This one showed Michael Swan in his final position, tied to the metal structural supports that ran across the ceiling, and facing down towards the floor. Somehow the photographer had managed to get high enough to capture the scene from parallel with the body. The image was ghoulish and dizzying.

      ‘So the end of the rope that ran the length of his body was then slung over the metal beams that ran perpendicular to the corpse, formed a final loop by passing back through the ankle knot to get his legs off the floor, and tied off at ground level at the base of the bookshelf.’ Callanach pointed to an old metal bookstand that must have weighed tons given the amount of paper on it. ‘Easily enough ballast to have stopped his body from crashing down. How much did Michael Swan weigh, Ailsa?’ Callanach asked.

      ‘A fraction under eleven stone. He was fairly slim so that would’ve helped. Still a lot of weight to lift that high though,’ she said.

      ‘Not necessarily,’ Callanach mused. ‘If the killer attached a weight to the free end of the rope it would have worked