Police arrested a 63-year-old man Monday for robbery and assault after he stabbed a male shop clerk near the Yaesu central exit of JR Tokyo Station.
According to police, the man, who identified himself as Morimasa Hattori of no fixed address, was spotted as he was stabbing Masaki Akitani, 28, in the neck and abdomen at around 3 p.m.
The clerk was in serious condition, investigators said.
Police said the suspect, who had been drinking, attempted to steal a boxed lunch worth 1,000 yen from a stand in the station.
Another clerk caught him in the act, and the suspect returned the boxed lunch and began to walk away, police said. Akitani went after him, apparently to hand him over to police, they added.
The clerk was then stabbed as he was going up a nearby staircase, police said.
Police rushed to the scene and apprehended the man.
According to investigators, Hattori has admitted to stabbing the clerk, but told police he did not know why he did so, saying he had not slept for about two days.