1) reveals the killer's role if he observes him at the moment of committing the crime or his victim
2) can replace the evidence planted by the killer at the crime scene with his own (even with very light evidence); if the killer does not use additional evidence, the thief can also plant his own (i.e., the main thing is that there are not three pieces of evidence at once).
i.e., the thief can always plant his own evidence (regardless of the killer's additional evidence) and very light evidence, such as this fire mushroom.
Added 1 minute ago
From whom? Why a black cloak? He would kill a dark knight, so is the cloak from someone's avatar?
Added 35 seconds ago
Wouldn't such obvious evidence be planted?