Police said Monday they arrested a man by mistake after incorrectly measuring the size of a folding knife he had with him during a fight with his father.
Under the Firearms Control Law, it is illegal to possess or carry various kinds of weapons ranging from guns to knives. Knives are regulated by blade sizes and the circumstances in which they are used. In the case of a folding knife, the blade must be less than 8 cm in length.
Later investigations found that the man, identified as construction worker Koji Motogi, 29, had a folding knife with a 7.6-cm blade, according to officers in the Saitama Prefectural Police.
Motogi was still played under arrest, with the charge changed to preparing to commit murder.
The father called the police at around 5:20 p.m. Sunday, saying he was having a fight with his son. When officers arrived at their home in the city of Hanno, Motogi was yelling "I'll kill you" while holding the knife in his hand, according to the police.
An officer measured the knife at the scene and determined that the blade was longer than 8 cm. But after Motogi was taken into custody at Hanno Police Station, officers found that the blade did not violate the law.
The police issued an apology and briefly released Motogi but then arrested him again.
According to investigators, Motogi admitted to carrying the knife to kill his father.