Henrik Karlsson breathed onto the lenses of his red-framed glasses and wiped them methodically, holding them up to the light from the window to check for smears. ‘I hate smudges,’ he said. ‘They’re so distracting. I keep imagining there’s somebody in my peripheral vision.’ His tonal accent was slight but definitely of Scandinavian origin, elongating and softening the ‘s’ sound. He fitted the spectacles onto his fleshy nose and sat down, placing one long leg over the other before studying Natalie with ice-blue eyes.

‘The killer left two separate messages, both written in blood?’

‘That’s correct.’ She handed him photographs of the messages left behind at the crime scenes.

His bottom lip protruded as he examined both pictures before placing them on the desk in front of him. ‘The children. Ages?’

‘The first, six months. The second, thirteen months.’

‘Both boys.’

‘That’s right.’

He didn’t move, his eyes focused on a spot some way in the distance. ‘Both victims were women in their twenties, similar build and married. Can I look again at their photographs, please?’ He put the pictures side by side and pointed at each in turn. ‘They have brown eyes although not exactly the same shade of brown. Their noses are slightly different, as are their lips, and their hair is of a different colour but a similar style – long and straight. The killer might be searching for women who remind him of one particular person. Ordinarily, if that were the case, the female victims would share more identifying features.’ He ran long fingers over his blond beard.

‘We discovered that Samantha dyed her hair. It is naturally chestnut-brown, the same colour as Charlotte’s.’ Natalie waited for him to continue.

‘Then he might be targeting women with naturally long dark hair and brown eyes. Perhaps they remind him of someone.’

‘Somebody he hates?’ Natalie asked.

‘Or loved or even still loves but feels that love isn’t being reciprocated. I understand he assaulted the first victim with a baseball bat found under the bed. That might have been opportune. He would have no way of knowing the bat was there unless he had entered the house on an earlier occasion. The second victim was killed with a knife you believe was purchased especially for that purpose. It would not surprise me to learn he took that knife to the first house to use as a weapon but was surprised by Charlotte and, instead, wrestled the bat from her to use against her. I think he intended to use the knife, and my reasoning is that, for him, it is important his victims bleed. He needs the blood so he can write his messages.’ Yet again he tapped the photograph of the blood-written messages.

‘That brings us to their significance. The first message he left was one word. “Why?” I believe this to be a question for either you, the police, or somebody who was close to him and who has caused him harm or upset – a lover, a sibling, a parent. I refer to the killer as male but they could be female. The majority of men committing murder opt for a gun, whereas far fewer women use a gun. Instead, they are more likely to use a knife, or indeed to strike their victim to death with a blunt object. Although I should point out that female knife attacks are generally against men, not other women, I would not discount the possibility the perpetrator of this crime is female.’

He nodded to drive home his point, and when he thought it was made, he continued. ‘The second message, another question, “Who?” This one seems once more to be directed at those investigating the crime. He’s asking the same question you yourselves are asking – who is responsible for this? If this is the case, he’s challenging the authorities. He’s bold and confident you won’t establish his identity. There’s another possibility: this question follows the first and is addressed to the same unknown – the lover, sibling or parent – as the first question, “Why?” If so, the meaning is obscure.’

‘You can’t hazard a guess?’

‘I could come up with several but they’d only muddy the waters. He’s asked two questions so far. As you know, there are five questions beginning with the letter W: Who? What? When? Where? Why? I fear he might ask all of them and there will be more victims. I also think the killer is in no hurry. He wants whoever these messages are addressed to to see what he’s capable of.’

‘Have I got this right? We’re searching for someone who’s on a mission to deliver a message to us, the police, or to somebody they know?’ Natalie asked.

Henrik turned his gaze onto her. ‘I believe so. He’s full of anger but also controlled. I suspect the frenzied attack on each victim wasn’t because the perpetrator hated them; it was to extract sufficient blood for the messages. Care has been taken with each stroke. See? The lines forming each letter slope and meet in the correct places. Look, here the W is perfectly formed. The lines, or upside-down V-shape attaching the uprights, have no gaps between them. The killer took time to compose each question and to make his writing neat. The messages are key to this.’

He paused to drink from a water bottle. No one spoke. When he was finished he carefully screwed the top back on before continuing. ‘And the victims. Why not target men or even older women? He has chosen women in their twenties, both with young children. It is a deliberate choice. I’m unable to fathom the reasoning behind it, as there are many explanations as to why he has done so. The perpetrator might be a female in the same age group as these victims who has lost a child and feels an uncontrollable jealousy towards those who have not, a man who has lost a lover or spouse… You see what I mean? There are several options.

‘Jealousy is a powerful emotion. There is one more thing. The murderer didn’t stab or beat the children. The bodies of the female victims provided the blood for the messages.’ He ran fingers and thumb down his beard once more, resting them on his chin before speaking. ‘He doesn’t want to hurt them, but it’s important to the killer that his victims have children who are abandoned near the scene of the crime. That might be meaningful.’

Lucy picked up on his last sentence. ‘The killer might have been abandoned?’

‘Or felt he was. That’s all I can give you for the moment. What you should mostly bear in mind is that the person you are hunting for is intelligent and careful – very careful. Chameleon-like. They are probably an expert at masking their reactions and feelings.’

With that, collecting his bottle from the table, he rose. ‘I’ll be upstairs for the next day or two. I’ll search through the files, speak to Forensics and see if there’s anything more I can offer you.’ He took three strides to reach the door and disappeared into the corridor.

Natalie addressed her team. ‘We have to return to the start with these victims and dig up some more information on both, talk to friends and families again. Go through witness statements. Bear in mind what you’ve heard.’

She returned to her desk and switched on her laptop. It was one thing having an idea of what the killer was doing – writing messages to an unknown other – but she was still no closer to establishing who that might be, and if the perpetrator was unconnected to the victims, it would be like hunting for a needle in a haystack.

The internal phone rang and Murray answered. ‘Great.’ He jumped to his feet. ‘CCTV camera outside a Lidl store picked up Finn Kennedy two minutes ago.’

‘I’ll come with you,’ said Lucy, leaping up and making for the door.

‘Take vests,’ shouted Natalie at their retreating backs. ‘He could be armed.’

She pulled up a map of the area around Lidl on her screen. If Finn was getting provisions from the store, he must be hiding out nearby. She called Ian across to help work out where the youths were. Any traction on this case was a positive, and she was going to make sure locating Finn and Hassan paid off.