Police in Tokyo have arrested a 52-year-old former police officer on suspicion of assaulting a man who tried to stop him from fleeing from a subway station after he allegedly groped a woman on a train.

According to police, the incident occurred at around 7 a.m. Monday on the Toei Shinjuku Line. Police said the suspect, Masao Shinada, who is now a company employee and a resident of Chiba City, allegedly groped the woman. She yelled at him and called for help after he got off the train at Jimbocho Station in Tokyo's Chiyoda Ward.

A station employee tried to hold onto Shinada but he resisted and started to run away. A man in his 20s saw the commotion and chased after Shinada, catching up with him at the top of a staircase. The two got into an argument and both toppled two meters down the steps. Police said the younger man fractured the right side of his skull and is in a serious condition.

Shinada was restrained by another male commuter on a nearby train platform for the Mita subway line.

Police said Shinada has denied assaulting the man and quoted him as saying he was just trying to shake him loose. He has also denied groping the woman on the train.

Shinada was a former security police officer for Internal Affairs and Communications Minister Sanae Takaichi. In July 2007, he was arrested on suspicion of groping a female college student aboard a train in Tokyo. At that time, he was sent to the prosecutor's office after he injured a male witness who saw him grope the victim. Although he was released without indictment on both charges of physical and sexual assault, Shinada resigned after being suspended from his security police duties that year.

© Japan Today