Police in Osaka say what is believed to be a gunshot was heard in the city of Suita on Sunday morning shortly after a police officer was stabbed and had his handgun stolen.
A 33-year-old man was arrested on Monday morning on suspicion of attempted murder and theft.
Police found evidence that one of the five bullets in the handgun had been fired.
They received reports of a possible gunshot heard near the scene of the crime about 20 minutes after the attack.
Investigators found that more than one person said they heard similar sounds.
There have been no reports of damage.