‘Okay, I’m stabbing. What’s your point?’ asked Erika.
‘Do you have an actual kitchen knife so I can demonstrate?’
‘Hang on.’ She got up, went through to the kitchen and found the box marked CUTLERY. ‘Here we go,’ she said, coming back into the living room. She put down the cardboard box, which contained eight knives of various sizes.
‘What do you use this for?’ he said, holding up a huge silver meat cleaver.
‘They were all Mark’s. He was the one who loved to cook.’
‘Okay. Imagine you want to stab me in the heart, and you pick that normal-looking kitchen knife,’ he said.
Erika picked up a kitchen knife which had a thick blade and a serrated edge. She held it, feeling its weight.
‘The average kitchen knife is not designed for stabbing,’ said Isaac. ‘They’re made for slicing, applying pressure down on the length of the blade. And if you wanted to stab me through the ribs, you’d have to turn the blade horizontal, to fit between them, and it would make the knife less easy to control. This knife would be more for the purpose.’ He picked up the long, serrated bread knife. It was older, with a smooth wooden handle which was worn away. It had belonged to Mark’s grandfather, who had been a stickler for his thinly sliced bread. Isaac handed it to her.
‘Imagine trying to stab me with this.’ He turned around so his back was facing her. She looked at his shoulders and then took the knife in her hand, feeling how well the smooth wooden handle sat in her palm. She raised the knife above her head. It was very long, and even though she and Isaac were the same height, she could see how high she would have to raise the knife to get the speed and heft to penetrate the thick muscle on his back.
‘It would be a challenge to aim, having to lift the knife so high.’
‘And your arm would naturally give the stabbing movement an arc,’ said Isaac, turning as she moved the knife down slowly so the point came close to the material of his sweater.
‘A shorter knife would be easier to control,’ said Erika, putting the bread knife down and selecting a small paring knife with a mother of pearl handle. It was fiercely sharp and had belonged to Mark’s mother. She’d bought it on a holiday to Thailand, back in the 1970s, when souvenir knives could be brought back on the plane.
‘A sharp paring knife like this would penetrate easily,’ said Isaac, taking it from her, ‘but it would be too short to actually reach the heart. I’m saying that a special kind of long thin knife or dagger was used to kill Vicky. And the person who did it used great precision and had upper body strength.’
‘Would the person have needed the same attributes to kill Sophia?’ asked Erika, putting the mother of pearl knife back in the box.
‘Not necessarily, but as I say, I’m not providing a hypothesis. I’m just giving you the facts…’
‘But it could be two different people who killed Sophia and Vicky,’ said Erika, sinking back down on the mattress. She picked up her glass and took a glug of the champagne.
‘There is something else,’ said Isaac.
‘What?’ said Erika wearily.
‘There was very little DNA found at the scene. We found Jasper and Tess Clarke’s DNA, which is to be expected at their house, and some other benign samples that we’ve run through the database. These could have been delivery people, friends of the couple, etcetera. We also were able to lift a latent saliva sample from Vicky’s left shoulder,’ he said.
‘How much saliva?’
‘It wasn’t a droplet. It was considerably more. When her body was found, she was wearing pyjamas and a sleeveless top, and this person’s mouth could have made contact with her shoulder. There was one millilitre of dried saliva swabbed from the surface of her skin.’
‘What’s that in layman’s terms?’ asked Erika.
‘A good bit of drool,’ said Isaac.
‘Do you have a DNA match on the saliva?’ she asked. Erika could feel her heart lift.
‘No. We ran it against all of the samples we were given, and the National DNA Database. We also took DNA samples from Tess, to eliminate her DNA from the crime scene. And it doesn’t belong to Jasper. Nor is it Vicky’s own saliva, which is something I wanted to rule out. Whoever it is doesn’t have a record. They’ve never given a sample.’
‘And it counts out Charles Wakefield, too, because his DNA was taken when he was arrested on Monday. And Shawn. He gave us a voluntary DNA sample. What else can you tell from the sample?’