Helsinki police suspect a 16-year-old boy of killing a 24-year-old man at Helsinki Central Station on Monday evening.
Police had earlier suspected seven minors of involvement in the killing, but as the preliminary investigation progressed one clear suspect emerged and he was taken into police custody on Tuesday.
Officers had quickly caught up with the other six members of the group at Malmi train station, where they had travelled by train shortly after the stabbing. All six were released on Tuesday afternoon after being interviewed by police, but one of the six is still suspected of assault.
Police said on Tuesday that the stabbing was preceded by a fight after the group of seven minors followed a separate group of three men into the tunnel entrance between tracks 1 and 2.
The situation escalated into violence that resulted in the stabbing and death of the 24-year-old victim, police believe.