Let's... take this point by point.

First of all, if we do assume that Valmont was killed in the sensory deprivation chamber, why was he there in the first place? Even if you think the knife was planted, that letter being forged seems, um, implausible. He went out with the intent to kill someone. You also have to wonder how he got all that dirt on him in the first place. Further, if the towel was put in the washing machine, all that dirt had to have come off, it makes more sense that it was used after whoever grabbed them went into the chamber to wipe any further dirt off, and that's why they're damp.

If a cut is made post-mortem, it'll bleed significantly less since the heart isn't bleeding, and even though there wasn't as much blood pooled beneath his body as there should be, there is still a fairly significant amount of blood. Finally, none of this explains the small bloodstain in front of Dylan's room.

[This was probably going a bit far to crush Adorabat's theory, but they need to clear the air and have a more solid order of events than this.]