A 21-year-old former Self-Defense Forces member arrested over a fatal police box attack in central Japan was carrying at least four knives, a sign the attack was premeditated, investigative sources said Wednesday.

On Tuesday afternoon, Keita Shimazu, a part-time worker, stabbed to death Kenichi Inaizumi, the 46-year-old head of a police box in Toyama city, and stole his handgun. Shimazu then shot and killed Shinichi Nakamura, 68, a security guard at a construction site nearby.

He was arrested at the scene after being shot by another police officer. He remains in critical condition.