Gillian Leak knew her work was getting to her when she kept seeing her son's face on the body of a brutally murdered child
Mrs Leak is a biologist who specialises in blood pattern analysis, getting a "buzz" from crimes where blood letting has occurred.
Her expertise was called upon by Mark Lundy's defence team, the British specialist giving evidence central nervous system tissue could have got on to Mr Lundy's shirt through contamination.
Lundy was yesterday found guilty murdering wife Christine and daughter Amber in August 2000 following a retrial ordered by the Privy Council. He was first convicted in 2002 but the Privy Council overturned that decision in 2013.
More on yesterday's verdict and reaction
Mrs Leak told the trial she had lost count of how many crime scenes she had examined where brain matter was spread around the scene - as it was at the Lundys' Palmerston North home.
She likened the job to solving a jigsaw but said the big difference was that jigsaws generally started with a complete picture to be recreated while murder scenes worked in reverse.
"... imagine you've only got the pieces without the box covering, so you tip out all the pieces on the desk and you've got to try and make sense of those jigsaw fragments," she said.
"At first it can overcome you because you don't know where to start but then you start to realise 'well, clip those pieces together, you've actually got a door'.
"So you recognise the door but you don't see the full picture still but you might pick out a tree. So you've got a door and a tree, you add that - what else does it mean?
"It's as you start to put the pieces together, more and more starts to make sense."
Too many child murders
Mrs Leak has worked on some of the most horrific and high-profile cases in England's north-east, including that of Peter Sutcliffe, known as the Yorkshire Ripper. Sutcliffe murdered 13 women and attempted to murder seven others between 1975 and 1980, mostly by hitting them in the head with a hammer.
She said while there were too many murders in general, she had been to far too many involving children.
"They've had their whole life ahead of them and it's been snatched," she said.
Mrs Leak has worked on a number of cases involving young girls being abducted and killed, one of whom "had gone to the shop to do some shopping for her mum and just disappeared".
It made 54-year-old Mrs Leak a lot more protective as she and her upholsterer husband raised their now adult children.
"Because you see the extreme end of society, obviously it's going to taint your view. You tend to be very careful on self preservation as much as their preservation, particularly when they were teenagers," she said.
"It was running them there and picking them up because they can't go on the bus."
Her children never rebelled against her being "precious about them", perhaps because she never hid what she did from them.
"I think because they'd had a degree of exposure to what I did, they understood why I can be precious.
"You didn't go into the gory bits but you didn't hide what you did, either. They probably grew up quicker than some of the kids in that sense."
"I used to apologise for being so restrictive but you can do it subliminally as well, in that you make a room in the house available for them to invite all their friends around, so you can still have all the social networking but I knew where they were."
Mrs Leak met her husband through her father - also an upholsterer - and both sides of the family live in the same area.
Their closeness, both physical and emotional, provides essential support to the family as Mrs Leak is on 24-hour call, and can be away for days at a time.
"When you're juggling school hours and meals and if you're out for two, three, four days at a scene, then somebody has to keep the home fires burning," she said.
Occasionally the lines between work and home become blurred; for Mrs Leak it was seeing her son's face on the body of an horrifically murdered child.
She had dealt with the scene, which involved two children, and attended the post-mortems of both without incident. But things changed when she headed for bed that night.
"I could see the boy's body with all his injuries but my son's head, which was a bit weird. This is the vision that I just couldn't get out of my head.
"This went on for a few nights. Every time I went to bed I had this vision of a mutilated child, basically, with my son's face.
"I realised what it was. It was because my son, at the time, was very similar in build, hair colour. My brain was associating the two."
Mrs Leak discussed it with a colleague, who immediately raised a scene the two had attended the previous year.
It was then Mrs Leak realised the child in that incident looked like her colleague's daughter.
"She'd obviously had exactly the same problem as me and not discussed it. That night I slept really well and I think it's because I'd discussed it."
She did not stop there, though; as the principal for scenes for her organisation she made it compulsory for all to go through a full debrief each time, and for it to be recorded in case notes that they had.
Mrs Leak has run a number of workshops on the subject at the International Association of Blood Pattern Analysts conferences but said many countries had not yet realised the importance of counselling for people dealing with such trauma.
People might wonder what drives Mrs Leak, who fell into her job by accident as a 17-year-old, to keep going back for more.
The answer, she says, is simple: "You want to solve the jigsaw.
"You don't take that weight on board because you want to see if you can work out what the picture is. That is your mission."
*Clarification - For the avoidance of doubt, please note that Radio New Zealand reporter Sharon Lundy is no relation to Mark Lundy.