"What does a guy need with all this stuff, anyway?" Yousuke says. "Stuff,", because he doesn't see a theme here. Financial records, gun replicas, medical textbooks—
"Kuwabara was something of a researcher," Naoto explains. "We met during an investigation; as our interests aligned, we maintained contact."
"'We'—including me?"
"Including you," Naoto admits. "In any case—occasionally, Kuwabara sent information he considered relevant. The estate has a room cluttered similarly, and with similar crates."
He hasn't noticed.
But he hasn't been looking, either.
"So you understand," Naoto says, "under a certain view, our involvement here would be considered highly questionable."