A 50-year-old man recently discharged from a mental hospital has been arrested for allegedly killing a 72-year-old woman by throwing her off a platform and onto the tracks at JR Ueno Station in Tokyo, police officials said Wednesday.

According to the Ueno station of the Metropolitan Police Department, the man grabbed the woman as she was waiting for a train just after noon Aug. 5.

The man, an unemployed resident of Haramachi, Fukushima Prefecture, grabbed the woman by the arms and threw her off the platform. The police said the man had just arrived in Tokyo before the incident. They are not releasing his name because he has a record of treatment for schizophrenia.

The woman, identified at her family's request only as a visitor from Kagawa Prefecture, and her sister had been waiting to catch a train to the Kusatsu hot spring resort in Gunma Prefecture. She died two days later in a hospital due to shock from bleeding caused by a fractured pelvic bone, police said.

Station officials grabbed the man and turned him in at the Ueno police station. Police found an 18-cm knife in his bag. He told them it was "for self-defense," they said.

The police admitted the man to a mental hospital in Tokyo because he was making incomprehensible statements to investigators. He has been arrested on suspicion of causing injuries resulting in death following his recent discharge, the officials said.

The Ueno station hopes to determine whether he is mentally competent and can be held criminally liable.

He reportedly told investigators that he had not slept for three days and felt "irritated." He also said he selected his target at random, they said.