‘Right. There have been some spectacular results since we started using it. Cold cases being solved. They’ve even caught serial killers with it in America. Some people bleat about human rights and privacy, but personally I think it’s my human right to live in a world where murderous bastards don’t get to roam unmolested in my community.’

‘Here endeth the sermon.’

Dave conceded with a rueful smile. ‘Yes, 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”?’