When Kusanagi got downstairs Yukawa was still in the kitchen. He was standing with his arms crossed, glaring at the sink.
‘Why don’t you just come out with it and explain to me what you’re thinking? Because if you don’t, there’s no way I’m giving you special treatment like this again.’
‘Special treatment?’ Yukawa asked, lifting an eyebrow. ‘Is that what you call it when one of your officers barges into my laboratory and involves me in yet another tangled, hopeless investigation?’
Kusanagi let his hands fall down to his hips and stared back at his friend. ‘I don’t know what Utsumi said to you, but it has nothing to do with me. In fact, if you wanted to check the house, why didn’t you just call her again? Why drag me into this?’
‘Because a real debate can only happen between two people with opposing points of view.’
‘So you oppose the way I’m running this investigation? I thought you said I was on to a “sure thing”.’
‘I have nothing against you running a proper investigation. I just don’t like it when people discard angles of attack just because they seem improper or unlikely. Even if only the slightest possibility remains that something might’ve occurred, one shouldn’t disregard it too easily. Don’t toss out the dirt.’
Kusanagi shook his head in exasperation. ‘So what’s the dirt, in this case?’
‘Water,’ Yukawa replied. ‘The poison was mixed into the water. At least, I think so.’
‘Now we’re back to the victim-washing-the-bottle theory.’ Kusanagi snorted.
‘I’m not concerned with the bottle. There are other sources of water.’ Yukawa pointed at the sink. ‘That tap, for one. Plenty of water there.’
Kusanagi stared back into Yukawa’s cool eyes. ‘You’re serious?’
‘It’s a possibility,’ Yukawa said with a shrug.
‘But Forensics found nothing unusual about the water line at all.’
‘Yes, Forensics did analyze the tap water. But they only analyzed it in order to tell whether the water left in the kettle was from the tap or from a bottle. And I understand they couldn’t tell the difference, because of all the tap water residue that had built up inside the kettle.’
‘But if there was poison in the tap water, wouldn’t they have found it?’
‘It’s possible that by the time they checked, the poison had already washed out entirely.’
‘But the victim only used bottled water when making coffee.’
‘So I hear,’ Yukawa admitted. ‘But who told us that, exactly?’
‘The wife.’ As soon as Kusanagi said it, he bit his lip and stared at Yukawa. ‘And of course you think she’s lying, though you haven’t even met her. What ideas has Utsumi been putting in your head?’
‘She has her own opinion, and she’s entitled to it. All I’m doing is formulating a hypothesis, based on objectively observable evidence.’
‘And does your hypothesis tell you the wife is the killer?’
Yukawa ignored him. ‘I gave some thought to the question of why the wife told you about the bottled water. There are two possibilities. One is that the statement “Mr Mashiba only uses bottled water” is false. The other is that it’s true. If the statement is true, no problem. The wife is simply doing her best to aid the investigation. I think Utsumi would still say the wife is guilty, but I’m not half as stubborn. The real problem here is if the statement is false. Firstly, because lying would suggest that the wife was somehow involved with the crime – but it also means that there’s some reason for her to tell that particular lie. So I considered the effect that her statement about the bottled water had on the course of the police investigation.’ Yukawa wet his lips and continued. ‘First, the police investigated the empties to make sure there was no poison in any of them. At the same time, they found poison in the kettle. This led to the assumption that it was likely that the killer put the poison in the kettle. Which naturally provides the wife with an ironclad alibi.’
Kusanagi shook his head slowly from side to side. ‘That’s where I don’t follow you. Even if she hadn’t given us that tip, Forensics would’ve checked the water line and the bottles. In fact, by telling us he only used bottled water, she actually hurt her alibi. For example, Utsumi still hasn’t given up on the idea that the poison was in a bottle to start with.’
‘That’s just it,’ Yukawa said. ‘Many people would think exactly the same thing as Detective Utsumi. It made me wonder if the whole bottled water testimony might be a trap laid to catch just that kind of person.’
‘Huh?’
‘Anyone who suspected the wife wouldn’t be able to let go of the idea that the poison was added to the bottled water, because they’d think there was no other way for her to have done it. But if she used an entirely different method to poison her husband, anyone still obsessed with the bottled water would be left spinning their wheels for an eternity, never reaching the truth. If that’s not a trap, what is? That got me thinking. If the husband didn’t use bottled water—’ Yukawa stopped suddenly in midsentence. His face was frozen, his eyes looking over Kusanagi’s shoulder.
Kusanagi turned around, then stood, as startled as Yukawa.
Standing there in the entrance to the living room was Ayane Mashiba.
SIXTEEN
‘Er, hello … we let ourselves in,’ Kusanagi managed after a long pause. He realized it was an idiotic thing to say almost as soon as the words left his mouth. ‘Here to check up on things?’
‘No,’ Ayane replied. ‘Just here for a change of clothes. Might I ask who that is?’
‘Oh, this is Yukawa. He’s a physics professor at Imperial University.’
Yukawa remained silent.
‘A university professor?’ Ayane asked, clearly puzzled.
‘And my friend, actually,’ Kusanagi explained. ‘He often helps our department with, er, scientific investigations … which is why he’s here today.’
‘Oh, I see,’ Ayane replied. Though she was clearly still puzzled, she said no more about him. Instead she asked, ‘Is it all right for me to touch things?’
‘Of course. You’re free to do whatever you like. I’m sorry we’ve taken so long.’
‘No need to apologize.’ Ayane moved towards the hallway. But after two steps she stopped, once again turning to face Kusanagi and the physicist. ‘I’m not sure if I’m allowed to ask, but what are you looking for, exactly?’
‘Oh, right,’ Kusanagi began, wetting his lips. ‘Well, we’re still having trouble determining the route by which the poison got into the coffee, so were doing some follow-up tests. I hope you don’t mind. We’ll be done soon.’
‘No, I don’t mind at all,’ she said. ‘It wasn’t a complaint, just curiosity. Don’t let me interrupt. I’ll be upstairs if you need anything.’
‘Right, thanks.’
Ayane gave Kusanagi a curt bow and turned to leave, but Yukawa spoke suddenly. ‘Might I ask a question?’
The widow stopped again. ‘Yes?’ The expression on her face made it clear that she did not trust this newcomer.
‘There’s a water filtration system on your sink here in the kitchen. I’m assuming you regularly change the filter, but do you remember when you last did that?’
‘Oh, that …’ Ayane came around to peer into the kitchen. She frowned as her eyes fell on the sink. ‘Actually, I don’t think I ever changed it once.’
‘Huh? Not even once?’ the physicist said with evident surprise.
‘I was thinking I should call the company and have them do it one of these days. The filter on there is the one they put in just after we moved in, so it’s about a year old. Which, if I recall what the serviceman told me, is right about when you’re supposed to change it.’