Double-murder suspect Takeshi Koizumi may have held a grudge against Health, Labor and Welfare Ministry bureaucrats because the system had euthanized a pet of his 34 years ago, but actually the Environment Ministry is responsible for destroying unwanted animals.

Koizumi, 46, has allegedly admitted to the fatal stabbings last week of former vice health minister Takehiko Yamaguchi and his wife, Michiko, in Saitama and the wounding of former vice health minister Kenji Yoshihara's wife, Yasuko, in Tokyo.

Police suspect there are reasons for the knife attacks beyond vengeance over a dog being killed three decades ago by public health authorities.

The Environment Ministry, and its predecessor, the Environment Agency, handle matters related to the Act on Welfare and Management of Animals, including pet euthanasia. The health ministry only deals with rabies cases.

According to an Environment Ministry study carried out in 2006, about 420,000 dogs and cats were brought to public health centers, and 95 percent of them were euthanized after their owners failed to claim them and no new owners stepped forward.

The fate of cats is generally worse than that of dogs. Only 1 percent of cats brought in to shelters find their way back to their owners, according to the ministry.

When owners bring unwanted pets to shelters, the animals are usually killed within a day. Lost pets are euthanized if not claimed within three to four days.

A ministry leaflet on lost pets warns that irresponsible owners are costing the lives of pets.