‘I don’t agree with the part about him being left-handed,’ Joe said.

Doctor Pratt looked round, surprised. ‘What do you mean?’

‘She will have cuts and bruises in the small of her back,’ Joe said.

‘Go on, Sergeant, enlighten me.’

‘The cuffs,’ Joe said. ‘We didn’t have those in the last murder. They are hard, uncomfortable, and if she was on her back, they would have dug into the skin as she struggled.’

‘But why is that important?’ Doctor Pratt asked.

‘You are assuming that he used his left-hand because that is his preferred hand?’

The doctor nodded.

Joe raised an eyebrow. ‘I’m thinking that he used his left hand because he was doing something else with his right. We thought at the scene that she was still alive when that debris was rammed between her legs, and so if he wasn’t raping her when she died, I reckon he was satisfying himself as he throttled her. It would have been much easier if she had been on her back rather than pushed against a tree or something, as it would have been easier to push down.’

‘And so the cuffs would dig into her back more,’ the doctor said.

Joe nodded. ‘That was my thinking.’

‘There’s only one way to find out,’ Doctor Pratt said, and then he waved at his mortuary assistant, who had been skulking in the corner. ‘Diener!’ he shouted. ‘Come here.’

Laura looked over to the young man sporting a ponytail and beard, his black T-shirt visible under his scrub suit. He looked like he spent his evenings on the internet fighting fantasy battles. And he didn’t look happy.

Doctor Pratt leaned towards Laura and whispered, ‘That’s their job title, dieners, but it is really just German for servant. Those who know that hate it.’

‘You could always call him by his name,’ she said.

The doctor’s eyes twinkled as he smiled. ‘This is much more fun.’

As the diener joined them, Doctor Pratt pointed to the body. ‘We just need to lift her, to check her back.’

The diener nodded but didn’t say anything in response. He scowled at Doctor Pratt and then grabbed hold of Jane’s arm and gave it a hard yank; there was no need to be gentle with her anymore. As Jane was rolled onto her side, Laura and Joe bent down to check her back.

Her shoulders and buttocks were pale, but the small of her back was dark from the lividity, where blood had settled as she lay there, undiscovered. Laura knew that the pattern meant that Jane hadn’t been moved recently to the spot where she was found. She had either been killed in that spot or been dumped there not long after her murder. There was an indentation in her back from the body block, a square piece of hard plastic placed under the body to make the chest jut out and the head tilt back, to make incisions easier. Just below that though, in the small of the back, just about visible in the purplish-blue of her skin, Laura could see the path of scrubbed and ragged skin, just as Joe had guessed.

‘Looks like you were right,’ Laura said to Joe, who just shrugged.

‘And her shoulders there,’ Doctor Pratt said, pointing to grazes and bruises on her shoulder blades. ‘Another sign that she was throttled on her back, those being where she was in contact with the ground.’

‘That doesn’t mean that he was masturbating though,’ Carson said. ‘It could just be that the killer throttled her using his strongest hand. And what about Don Roberts? Is he left-handed?’

‘Are you still going with that theory?’ Joe said.

‘Not as the main theory,’ Carson said, ‘but I’m not going to rule it out until we have to.’

Joe looked at Doctor Pratt. ‘Can we be sure it was strangulation?’ he said.

‘As opposed to what?’

‘Her mouth was jammed full of leaves and dirt,’ Joe said. ‘Perhaps she suffocated?’

The doctor pointed at the dead girl’s neck again. ‘She was probably alive when those were inflicted, and so my best guess would be strangulation. Also, it would have looked worse when you found her, because her tongue and lips will have swollen as she rotted in the woods, and so it might not have been quite as jammed in there when she died. It’s possible that the hand marks on the neck are from when he restrained her, but we won’t know until we open the neck and check whether the hyoid bone is fractured. If not, then yes, she probably suffocated.’

‘Does it make a difference, Joe?’ Carson asked.

Joe thought about that. ‘I think it makes it less likely to be a random sex attack if she suffocated,’ he said. ‘Throttling is an aggressive, sexual act. It isn’t uncommon for it to be a turn on for sociopaths. Gorging? It doesn’t have the same hands-on feel to it, if you know what I mean.’

Doctor Pratt chewed on his lip for a moment, and then he pointed at Laura. ‘Could you just pop onto the spare table.’

Laura looked at the other steel table further along in the room. ‘Do I have to?’ she said.

‘Will it help the investigation?’ Carson asked.

‘It could do,’ the doctor replied.

‘McGanity, get on the table,’ Carson said, and moved towards it, waiting for the show.

Laura took a deep breath and closed her eyes. ‘All right,’ she said, and then gripped the side of the mortuary table as she clambered on. The table was cold through her suit and her feet clanged loudly. She tried not to think of all the others who had been there before her. As she put her head back, her hair spread out over the metal.

‘If my left hand was my strongest, and the victim was on her back,’ Doctor Pratt said, ‘which side would I go to in order to throttle her?’

Carson looked at Joe before turning back to Doctor Pratt. ‘McGanity’s left, your right, so that your left arm is over her, pressing down.’

Doctor Pratt nodded and went to stand by Laura’s side. Laura watched as his left hand went to her neck. She swallowed as his hands went around her throat, pressing gently.

‘Look how even my hand is around the neck,’ the doctor said. ‘The curve of my hand, my index finger and thumb, are right under her jaw, and I could push right down, if I wanted to. She would find it hard to move her head.’ He smiled down at Laura. ‘Which, of course, I wouldn’t do.’

Doctor Pratt stepped away and then went over to the other side. Laura closed her eyes for a moment as she felt his hand go around her neck once more.

‘Look at my left hand now,’ he said. ‘I have to contort my arm to get it evenly around her neck, because my left arm is by her side, not over her. I could move her head towards me, I suppose, but the pressure would be different. I would be pushing the head back, not down, and so Laura would be able to move her head around, perhaps make it harder for me to throttle her. And so the most natural way for me to throttle someone from this side with my left hand is to have my hand tilted, so that the tips of my fingers are right under the jaw, more vertical, with my thumb lower down, so that the pressure comes from the base of the thumb, not the curve of the hand.’

‘You could straddle her,’ Carson said.

‘I could,’ Doctor Pratt said, ‘but the killer didn’t.’ He pointed towards Jane Roberts. ‘Look at the bruises from the killer’s thumb. They are much lower down than the bruises from the fingers, which suggests that the killer was to her right side, to the left from the killer’s angle.’

‘Why make it difficult for himself?’ Carson said.

Doctor Pratt pointed towards Joe. ‘He got it right. It leaves his right hand free to relieve himself.’

As Doctor Pratt stepped away from the table, Laura slid off and back onto the floor. As she straightened herself, she saw the diener smirk at her, recognising her discomfort. She turned away.

‘So once I’ve dissected the neck, I’ll know for sure,’ Doctor Pratt said.

‘Will you do that first?’ Carson asked.

The doctor tutted. ‘Everything in its proper order, Inspector. Got to pop the skull and empty the chest cavity first. Are you going to wait around?’