The Devotion of Suspect X - Keigo Higashino [98]
“So,” Yukawa was saying in a low voice, “do you believe this testimony of Ishigami’s? Do you buy his story?”
“As a detective, I see no reason to doubt it,” Kusanagi said after a beat. “We’ve been able to corroborate his account from several different angles. I did some canvassing in a local park near Ishigami’s apartment where there is a public phone. That’s where he claims to have gone every night to call Yasuko Hanaoka. Turns out there’s a grocery store near where the phone is, and the proprietor there saw someone matching Ishigami’s description. He remembered him because not many people use public phones these days. He claims he saw him making calls there on several evenings.”
Yukawa slowly turned around to face Kusanagi. “That’s what you think as a detective. I asked whether you believe him. I don’t care about your investigation.”
Kusanagi nodded and sighed. “To be honest, it doesn’t feel right. There are no holes in his story. It all makes sense. But I guess I’m just having trouble imagining him doing all those things. Of course, when I tried to tell the chief that, he didn’t want to hear it.”
“I’m sure your superiors are happy now that they’ve got someone to charge with a crime. Why would they want anything else?”
“Things would be different if there were even one piece of the puzzle that didn’t fit, but there’s nothing. It’s perfect. Take the fingerprints left on the bicycle. He claims he didn’t even know the victim got there by bicycle. Nothing strange there. Ishigami’s testimony supports all the facts. With that kind of momentum, there’s nothing I could say to turn the train around at this point.”
“So, you don’t buy it, but you have no choice but to go with the flow and accept the conclusion that Ishigami is your murderer.”
“Look, I know you’re not happy about this either, but don’t take it out on me. Aren’t scientists supposed to shelve their doubts in the face of logical arguments? Wasn’t it you who told me that? I thought you were all about facts over feelings.”
Yukawa shook his head—a barely perceptible movement—then came to sit down across from Kusanagi. “The last time I met Ishigami, he presented me with a mathematical conundrum,” he said. “It’s a famous one, the P = NP problem. Basically, it asks whether it’s more difficult to think of the solution to a problem yourself or to ascertain if someone else’s answer to the same problem is correct.”
Kusanagi frowned. “That’s mathematics? Sounds more like philosophy.”
“Bear with me. By turning himself in, and giving you his testimony, Ishigami’s presented you with an answer that, no matter how you look at it, has to be correct. If you just nod your heads and say, ‘Okay, sounds good to us,’ you’ve lost. Really, what you should be doing is putting all your efforts into determining whether his answer is correct or not. It’s a challenge. You’re being tested.”
“And like I said, we looked into it. Everything backs up his story.”
“All you’re doing is tracing the steps of his proof. What you should be doing is looking to see if there aren’t any other answers that might fit what you know about this case as well. Only if you can prove that there are no legitimate answers other than the one he’s offered can you say that his is the only solution to the problem.”
Yukawa’s irritation was plain from his unusually hard tone. Kusanagi had rarely seen the levelheaded physicist this agitated.
“So you think Ishigami’s lying? He’s not the murderer?”
Yukawa frowned and lowered his eyes.
“What’s your basis for saying that?” the detective went on. “If you’ve got a theory of your own, I’d like to hear it. Or is it just that you can’t bear to think of your old friend as a killer?”
Yukawa stood and turned his back to Kusanagi.
“Yukawa?”
“It’s true. I don’t want to believe it,” Yukawa said. “Like I said