But Koishi did have a "thought".

Being aware of that, she was able to make a decision.

She realized it'd be bad if people found out that she killed Reisen.

Even a mindless machine can have "awareness" and "judgment", after all.

Before I rushed to the scene, she stole Reisen's cell phone and hid behind the partition.

Realizing that she had to do something or get caught, she made that phone call to escape.

She continued to make chit-chat with the custodian.

Even if I couldn't hear her, Reisen was still alive and could've attacked her, but she wasn't afraid.

There wasn't the slightest bit of unease in her voice on the recording.

Naturally.

Koishi lacks the very concept of unease or panic.

That heartlessness bore fruit, and soon I left the scene.

Koishi returned Reisen's phone and fled outside through the door, now opened by the custodian.

This is the entire truth that XX-sama deduced from my testimony.