A woman was fatally stabbed at a convenience store in the suburb of Kodaira, western Tokyo, on Friday afternoon, local police said.
A man identified as 37-year-old Naoki Oyama, from the city of Saitama, was arrested on suspicion of attempted murder shortly after he fled the scene.
The charge was changed to murder after the victim was confirmed dead.
The woman was later identified as 36-year-old Yoriko Osada, an insurance saleswoman residing in the city of Kawaguchi in Saitama Prefecture.
She was attacked at a FamilyMart Co. store around 4:10 p.m., police said, adding that the 48-year-old male manager of the store, who tried to stop the attack, was stabbed in the chest.
Osada worked at a life insurance firm that had an office on the third floor of the building in which the convenience store was housed.
Police said that the woman was Oyama's former girlfriend, adding that it appears as though she was attacked after refusing his offer to resume the relationship.
Investigators said the woman had entered the store first, with Oyama following on her heels.
Although they talked at first, the suspect suddenly pulled out a knife and stabbed her in her side. Oyama ran out of the store but a local resident caught him.