Umm... I think I've pictured together what happened.

Starting off, I think the killer didn't kill Valmont in the dorms, but somewhere else. Since the water in the sensory deprevation room was weird, wouldn't Valmont have been killed in the sensory deprevation room? The two didn't have to be in the dorms for Sonic to miss 'em.

They... um, maybe the killer wiped off whatever was on Valmont with the towel in order to cover their tracks. And- and then they waited for a while for the bleeding to stop. They put the towel in the angry washing machine to try and get rid of any evidence it had on it. After Valmont stopped bleeding, the killer took him to the dorms.

The killer then cut Valmont's neck to try and get it to bleed in order to try and fake a crime scene. Valmont's body wasn't bleeding much, which is why there's so little blood. The killer dragged Valmont to the playground and set a hunting knife on him for whatever reason and went back to the dorms.

Then, the killer dumped paint in front of the dorms, dumping the red paint last and then entering their room.