You go left...

 

Into the room with the open door.  You walk in and see a bookshelf on your left and think you see the light from a computer ahead. You go towards it, the light from the hall windows shines into the room.

 

You think you see writing on the wall that seems to be glowing. You remember as a child that glow in the dark things tend to require total darkness to be visible, the windows in the room are shut but the light from the hall makes it hard to read. You doubt the writing is important to finding the missing murder weapon, but you are curious to know what it says.

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Do you shut the door to read the writing or leave the door open?