"El, every pair of three years is on the third floor. And the school building is... three floors."
"... you mean on top of that... there's only the roof"
"Yes, the killer snuck up the stairs carrying the body, carefully unlocked the candlestick so as not to make a sound, and finally escaped to the roof."
"Hmm. But why was that a mistake?
"Well, didn't you tell Elle about the conversation you had with the guard?"
"Hmm. I'm not listening."
Gaius shrugged his shoulders and apologized for the bad looks.
"Sorry, sorry. Then you don't know the truth about the case."
"Well, that's good. What happened to the guards after that?
"Yeah. The guard checked each classroom with a lantern to see if there were any abnormalities, and after checking every pair for three years, he headed up the stairs... I went up the stairs."
"Um. So?
"The guard lit the door with a lantern. Then the candlestick key was unlocked. Usually there's a key that's supposed to be closed. So the guard felt unusual and opened the door."
"That's where you ran into the killer!?
"No, the guard tried to illuminate the edge of the roof with a lantern. Because I thought the guard's head might have had a suicide volunteer breaking into the roof..."
"Well, if a suicide candidate breaks into the roof, there's one thing to do, not just jump off the edge of the roof to the ground."
"Yes, that's why the guard only focused on the edge of the roof."