In a Facebook posting on Sunday, Arhinmäki, who is known as a strong supporter of street art and as a creator of graffiti in his youth, apologised for his “stupid fooling around”. He is a former politician and chairman of the Left Alliance and served as a minister for culture and sports in 2011-2014.
Police are investigating the act as vandalism and interference with rail traffic, which had to be temporarily halted because of the incident. The rail tunnel is used by cargo trains running to and from a Helsinki port.
It wasn’t immediately clear whether Arhinmäki would face legal charges.
“I have committed a crime and bear full responsibility for it,” Arhinmäki told YLE, but has refused to resign from his post and the Helsinki City Council where his Left Alliance party is backing him.
The case has caused uproar and debate among Helsinki citizens on social media with a majority condemning — but some also fiercely supporting — the actions of the deputy mayor who is in charge of culture and leisure affairs in Helsinki, a city of 650,000 inhabitants.
The Finnish capital spends an estimated €650,000 ($1,167,514) annually to remove illegal graffiti throughout the city and is currently seeking to establish additional sanctioned sites for street art.