At that moment... the culprit was still inside the boiler room.

Reisen

The boiler room is large and confusing, so there were plenty of places to hide.

Reisen was pointing at the exit so I thought the culprit had already escaped, but...

If she was actually pointing at the partitioning screen next to the exit...

If she was trying to tell me where the culprit was hiding......

But in that case, they would've been making that phone call right next to you while you tried to break down the door!

How come you didn't hear their voice?

They were speaking quietly, and the boilers were very noisy.

I was in a panic, too, so I must've missed it.

This theory explains the long phone call as well.

The culprit needed to get out of the boiler room, but I'd see if they came out from behind the screen. That's why they stretched out the call.

Because the custodian's line was taken, I left the boiler room to go get someone. That's exactly what they were waiting for. Of course, there was a chance that I could've used the phone to call some other kappa, but I suppose that risk was pretty low.

The phone they used was probably Reisen's, for the record. I assume they stole her phone to call the custodian and then returned it before fleeing.