Jun'ya Tokitsu, immersed in his own spotlight and bursting with the urge to explain himself, naturally failed to notice the subtle looks everyone else was exchanging.
He described in detail how to secure the lock from this side of the door, using the door's structure to disguise a room that had never actually been locked as one that had been tightly bolted shut with a simple door-closing motion.
"...You only need to expose the base of the screw, then use the pressure of closing the door to press the contact surface back into the lock cylinder. It's a very simple setup." Having demonstrated it, Jun'ya Tokitsu confidently let go, then patted the tightly shut door, which looked every bit like it had been locked from the inside. His face was full of self-satisfaction. "Well? It's quite a feasible plan, isn't it?"
He turned around, glanced at Natsuki Koshi, who had her arms crossed and an unpleasant expression on her face, then nodded in her direction. "And the culprit couldn't possibly have been you, the last 'suspect' to leave."
"Calling me a suspect again?" Natsuki Koshi raised an eyebrow.
"The fundamental purpose of this setup was to confuse everyone about the order in which they left and closed the door. If the culprit had been the last person to leave, that would mean placing themselves under suspicion as well, which goes against the logic behind the trick." Jun'ya Tokitsu continued along the path of his analysis, his thoughts seeming to gradually return to the past.
If the culprit had been the last person to close the door, there would have been no need for such a complicated design. Or rather, it could not have provided testimony beneficial to them. The culprit had to be someone who needed to reverse the order