The shooting incident in central Japan occurred despite the country's tight gun control laws and strict regulations for possessing firearms.
National Public Safety Commission Chairperson Tani Koichi has said Aoki Masanori, who allegedly killed four people with a shotgun and a knife in Nakano City, Nagano Prefecture, is a legal firearm owner.
Tani told reporters on Friday that the government will consider ways to ensure that firearms are used safely once the case is closed.
In order to own a firearm, people need to obtain a license from a local public safety commission. The license should be renewed every three years.
Gun expert Tsuda Tetsuya says anyone who is 20 years of age or older without mental illness or not a risk to harm others can obtain a license to possess a shotgun after passing exams.
He says that's why most of gun crimes by ordinary citizens in Japan involve shotguns.
But he added that gun ownership is on the decline because regulations have been tightened to limit the eligibility in the wake of criminal cases involving shotguns.
Owners are required to have a special locker to keep their firearms and undergo an annual inspection.
A regional hunters' association that covers Nakano City says Aoki is one of its roughly 170 members.
Members of a regional association usually belong to a municipal association as well.
But Aoki did not belong to the Nakano association and is not believed to have taken part in activities to eradicate harmful wildlife.