The Southeastern Finland Police Department said it suspected a 23-year-old local man drove to the scene around midnight on Saturday, took a hunting rifle from the trunk of his car and fired four or five shots.
The suspect, who has criminal record of violent offences, was detained at the scene. The motive for the killings remained unclear.
“It looks like the victims were chosen at random,” Detective Inspector Saku Tielinen told a news conference, adding that a political motive seemed unlikely.
Victim Tiina Wilen-Jappinen was chairwoman of Imatra City Council. The other two women were journalists from a local newspaper, the police said.
“She (Wilen-Jappinen) was liked, nice and bright person. This is truly shocking,” Mayor Pertti Lintunen told the newspaper Helsingin Sanomat’s online version.
The gun was a permitted hunting rifle but it did not belong to the suspect, police said.
Finland shares an 833-mile (1,340 km) border with Russia and has sought exceptions from proposed European Union restrictions on firearms, citing defense needs.
Around 28,000 people live in Imatra.
“Finland is one of the safest countries in the world, but unfortunately acts like these are still possible even here,” Prime Minister Juha Sipila said in a statement. (Courtesy Reuters)