They had to be looking at the door the whole time it was open.

Only 10 seconds passed between me opening the door and hearing the scream. It should've been impossible to grasp the contents of the message in that time.

In other words—

The culprit wasn't even looking

where they stabbed Reisen.

Could a murderer with killing intent not watch what they were doing at the instant they stabbed someone to death?

Impossible.

The fact that they were able to make the call can only mean that they had no killing intent.

So, what? An accident?

The culprit had the ability to hide themselves, and Reisen just happened to get a screwdriver stuck in her neck?

Yeah, no. The case tells a different story. Reisen knew the culprit was there, so it makes no sense to believe that she got stabbed in the neck by accident.

"There was a murder without killing intent."

I... and probably XX-sama as well... could find no other explanation for this case.

That is...