Sillanpaa was born in 1968 and was a student in Helsinki. On February 21, 1999 she went to a shooting range on Albertinkatu, hired a pistol and ammunition as a customer, and shot four men. Three died: the club's twenty-three-year-old supervisor, a twenty-five-year-old car mechanic, and a thirty-seven-year-old man. One survived.
She had no connection to any of them, no history of violence, and no record. She left, was identified from the club's records within hours, and was arrested.
She was examined and found to be suffering from a psychotic illness. On October 11, 1999 she was found not criminally responsible and was committed to the Niuvanniemi state mental hospital at Kuopio.
No motive has ever been established, by the court, the psychiatrists or the police. That is the case: a woman with no history walked into a shooting club, rented a gun over the counter, and killed three strangers.
The killings led to changes in Finnish practice on the hire of firearms to walk-in customers. This is a single act, not a serial case, and it is in the archive under that classification.