The guy known as D lives in Ba Dinh district, said the police.
Foreign victims of the assaults were invited to the police station to identify the suspect.
K.M.C, an Irish woman, said that she was sexually assaulted by two men while walking down Dang Thai Mai street in Tay Ho district on February 20. She confirmed D was one of the two youngsters who attacked her that night.
However, D pleaded not guilty to the crime.
The police said they are investigating 25 other young people believed to be closely tied to the case.
VOV.VN has learned that a group of young men aged 15-20 were said to have carried out sexual assaults against foreign women living in Tay Ho district of Hanoi capital in recent times.
They normally drove unmarked motorcycles past the women walking down streets such as To Ngoc Van, Quang Na, Quang Ba and Dang Thai Mai and committed violent sexual assaults on sensitive parts.
A victim even said the suspects strangled her, threw stones at her and snatched her belongings.
Tay Ho district is known as a place where a lot of foreigners rent properties to work and live in Hanoi.