A 29-year-old man who has admitted to poisoning cats in Kanagawa Prefecture last November said he was driven by his long-standing hatred of felines.
"I always disliked cats," police officers quoted the man as saying.
The case was referred to prosecutors on Monday.
The Sagamihara man is suspected of killing three cats by placing poisoned cat food near the Sagami River on Nov. 17 and 24.
Five cats were found dead in the area that month, along with cat food laced with methomyl, a powerful insecticide.
The man emerged as a suspect after police tracked an online message board post that read, "I killed a cat with poisoned food."
The police searched his home in January and found images on his computer and smartphone of cats that ate the poisoned food, investigators said.