The Finnish Transport Infrastructure Agency told public broadcaster YLE on Wednesday that cleaning up graffiti illegally painted by Paavo Arhinmäki, one of the four deputy mayors of Helsinki, cost the city around 3,500 euros ($3,830).

Arhinmäki, 46, and a friend were caught by guards in a rail tunnel in eastern Helsinki on Friday just after they had completed graffiti, which Finnish street art experts said looked partly inspired by works seen in New York City in the 1970s.

Finland’s largest newspaper, Helsingin Sanomat, published a photo of the large-scale graffiti in a tweet.

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, apologized for his “stupid fooling around.” He is a former lawmaker 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 on Monday, 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 in 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 euros ($710,000) annually to remove illegal graffiti throughout the city, and is currently seeking to establish additional sanctioned sites for street art.