Tony Hill u Carol Jordan 08 - Cross and Burn

but here beginneth the lesson. So, I ran a check for familial DNA. Basically, the computer analyses the alleles and comes up with a list of people who have a degree of commonality. So, number one on the list has most alleles in common, and so on, right down to number one thousand, three hundred and forty-nine, in this case. Now, experience shows that if you’re going to get a familial match, it’s going to be in the top thirty. We’ve got a little formula that incorporates the genetic match, the ages of the people concerned and their geographical location, and that gives us a likelihood of a particular relationship. But even before I had to use the formula I spotted someone in my top three who lives within a dozen miles of where your sample was taken. When I looked more closely, what do you know? I got what I consider a definite hit.’ He neither looked nor sounded happy about it. ‘The family member is a woman. It’s my opinion, based on the DNA analysis, that this woman is a close relative of the man – and it is a man, by the way – whose blood was deposited on Nadzieja Wilkowa’s jacket.’ He leaned across the desk and clicked a tab on his screen. Up popped a pair of the familiar DNA profiles, one above the other, with their jagged peaks at irregular intervals. ‘See for yourself. Where the alleles align, that’s the key factor. So, how close is this genetic relationship? Now, we all have around five alleles in common with any given person. But the direct relationship of mother to offspring means there would be at least ten alleles from the crime stain which must have come via the mum.’ Dave tapped each of the allele peaks with the tip of his pen. ‘Eleven, you see?’
    ‘I believe you, Dave. And so will a court. You seem really anxious about this. I don’t know why. It’s not like it’s ground-breaking science.’
    ‘The integrity of the science is not what’s bothering me. Well, it is, but not for the reasons you’re thinking.’
    Paula shook her head. ‘I’m a simple copper, Dave. I can’t do cryptic crosswords. Just tell me straight. What’s the issue?’
    He looked pained. ‘The identity of the person on the database. It’s a woman called Vanessa Hill.’
    Paula gawped at him, her mouth open. She couldn’t quite credit what she’d heard. ‘Did you say “Vanessa Hill”?’
    Dave nodded, his expression miserable. ‘I did.’
    ‘What’s her DNA doing on the database?’ Paula clutched at what she knew was a broken straw.
    ‘She was arrested and charged over the stabbing, remember? Even though the charges were dropped pretty much overnight, the DNA stays on the record.’
    Paula shook her head, disbelieving. ‘Could it have been transferred by someone else? Planted, even?’
    ‘It’s very doubtful. The way it’s soaked into the threads and the cloth around the button – it would be hard to replicate that unless you had a liquid sample. And if you were trying to fit him up, wouldn’t you leave the bloodstain somewhere more obvious? We could have missed that, even on a detailed second pass. If you hadn’t been counting buttons, it could easily have gone unnoticed.’
    ‘There must be a mistake. You’ve got to run the test again.’
    ‘I will, of course. But I’m confident the answer will be the same. And I’ll also run a mitochondrial DNA test. That’s the DNA that comes direct from the mother to the child. If that’s a match, there’s no room for doubt.’
    ‘What if she had another child? A sibling he doesn’t know about?’
    ‘You’re reaching, Paula. That hypothesis breaks down as soon as we test his DNA, unless it’s his secret identical twin. Which starts to sound like The Man in the Iron Mask .’
    Paula stared at the screen, willing it to metamorphose into something different. ‘Can we keep this to ourselves?’ She saw the look of horror on Dave’s face. ‘Not completely, obviously. But at least till you’ve double-checked that there hasn’t been a cock-up with the test. Or with the database. And you’ve checked the mitochondrial DNA. And’ – she pointed to the evidence bags she’d delivered – ‘you expedite the evidence from this latest murder and see whether that gives us a more viable suspect.’
    He sighed. ‘I’m not happy with this, Paula. This is important evidence in a murder inquiry.’
    ‘Evidence that we both know makes no sense.’
    He rubbed his soul patch between finger and thumb. ‘The science doesn’t lie, Paula.