There's a window in the boiler room door. I think Reisen probably saw someone through it.

The culprit, I assume.

I just shrugged, wedged the storeroom open with a door stopper

and took the whiteboard inside by myself.

I wasn't really paying attention, but I could tell from the sound that the boiler room door was also open.

The boiler room is really noisy, after all.

If you leave the door open, the sound can be heard all the way to the storeroom.

Right after I took the whiteboard inside, I heard Reisen's scream from the boiler room.

I ran out of the storeroom and over to the boiler room, and...

I found Reisen lying on the floor, covered in blood, with the murder weapon stuck in her neck.