through it.
“I’m impressed that you knew it was mine.”
“At least half of it was nothing more than a gamble.” I explained how I had gone to N** Mountain to look for her body and what line of thought had brought me here.
†
What had the killer been thinking?
I’d begun by imagining the killer after he’d dropped the notebook.
Why had he written the notebook? To help him remember? To keep a record? I was sure he had read it over and over and that he attached great value to it, so he must’ve noticed that the notebook was missing.
Where had he kept the notebook? Either in his pocket or in his bag. Considering he had dropped it, probably in his pocket. Maybe he had washed his hands in the bathroom and dropped the notebook as he pulled out his handkerchief.
So when had he noticed it was missing? Ten minutes later? A few hours after? I was sure he had noticed it before the day was out.
He would have tried to figure out when he had last read it, the last time he was sure he had it. Then he would have retraced his steps, figuring out where he was most likely to have dropped it.
And I was willing to bet he had narrowed it down pretty well—mostly because I imagined he looked at it quite often. Every time he felt his thoughts growing dark, he would calm himself by reading the notebook. And if he read it that often, he would be able to pinpoint a narrow range of places and times he could have dropped it.
Then the killer must have looked for it, staring at the ground trying to find it.
But he would not have found it there. So the killer must have thought that someone picked it up. If someone were to read the book, he was finished—the police would search for the third victim and find the body. That wasn’t a problem in itself; the problem came if they managed to lift his prints from the notebook or match his handwriting.
If this had happened to me, what would I think? I certainly wouldn’t kill a fourth victim. The police might be investigating nearby. After all, the notebook had been dropped someplace the killer went on a daily basis. The police would assume he lived nearby. He couldn’t take that risk.
But a few days had passed, and Mizuguchi Nanami’s body still had not been found—because Morino and I had not turned over the notebook to the police.
The killer had been watching the news every night, waiting for them to find her body. He would not kill again until he was sure it was safe … but Morino had gone missing.
Discounting the possibility that Morino’s disappearance was just some sort of prank, I tried to figure out why the killer would act. If I were the killer, why would I choose a fourth victim?
* I couldn’t bear to wait any longer.
* I got overconfident, sure I wouldn’t be caught, and underestimated the police.
* I didn’t care if I got caught.
* I thought that nobody had picked up the notebook, that nobody had read it.
* I thought that whoever picked it up had not believed it.
Or perhaps he had actually not noticed that he’d lost the notebook. These were all possibilities … but I decided to bet on another theory. I believed the killer had thought as follows:
* Someone picked up the notebook but was unable to read it. That’s why they haven’t given it to the police and Mizuguchi Nanami’s body has not been found.
The shop master listened to all this, nodding with interest. “So why did you think it was me?”
I took the notebook back and opened it. I showed him where my sweat had smudged the writing, leaving it illegible. “You knew what kind of ink you’d used, and you knew that if it got wet, nobody could read it. I theorized that the killer had assumed he’d dropped it outside, not in the shop. Morino told me it was raining hard when she found the notebook; it seemed likely the killer knew he had dropped it while it was raining.”
It was only natural that the killer would assume that if the notebook had been picked up in the shop, it would have been given to