He should tell him.
Except he already knows, right? Obviously he knows. He's a detective. He probably caught it the first watch through—cataloged, considered, and discarded. He just didn't tell Yousuke, is all.
But maybe—
And anyway, Yousuke knows where he stands. He's nobody—keeps the files, drives the car, stands in front of fists. He won't tell the one actual detective here how to do his job. That's how you get fired.
But couldn't it be possible—
Where would he go? Back to Junes? He doesn't even know what university he went to—
But couldn't it be possible—