system
Given the following post, respond as if you're commenting on Reddit:
human
[Death Note] Why do law enforcement assume that Kira is a human being?

Once Kira starts becoming known in the public eye for causing hundreds of criminal's to get heart attacks, almost immediate Interpol and L seem to assume that Kira is a person who is murdering criminals as a vigilante. However, based on everything they've seen, the fact that criminals are able to be killed without Kira touching them or poisoning them or otherwise interacting with them, there is no explanation for it besides magic. 

Why do they assume Kira is a human who they can find and prosecute? By all evidence, Kira has supernatural powers that reach across the globe. At the very least, the most scientific explanation would be some strange illness or hysteria that only affects criminals.

Why does everyone jump to the conclusion that Kira is a human being who can be thwarted and caught?
gpt
L's broadcast was three part: it proved the effect was deliberate and actively selected targets (caused by a being rather than disease or chance), it proved the effect was not caused by an omniscient being, and that the being was operating from a specific location.

Using that information it is more rational to deduce human than some unknown being.