Sanna Riitta Liisa Sillanpää was born on April 15, 1968, in Finland. She grew up in a typical Finnish family. Details about her childhood and family life are limited. Sanna studied hard in school and later pursued a higher education. She earned a Master's degree in computer science.

After finishing her studies, Sanna became an IT worker. She found a job at Fujitsu Finland Oy in Helsinki. In her role, she worked on various projects related to information technology. Sanna was known to be skilled in her profession.

On 21 February 1999, Sanna Riitta Liisa Sillanpää shot three men at a shooting range in Albertinkatu, Helsinki. She used a rented 9mm Beretta 92FS semi-automatic pistol. Among the deceased was a 23-year-old supervisor of the shooting club. In addition to the three killed, one man was injured and would suffer lifelong consequences from the attack. One other person present during the shooting was unharmed.

After the incident, Sillanpää left the shooting range and made her way to a city bus. She traveled to the Helsinki-Vantaa Airport while carrying the gun and ammunition. At the airport, she attempted to buy a ticket to an undisclosed location. Police apprehended her four hours later as she was about to board a flight to London. Before her arrest, she discarded the gun in a trash can at the terminal, which a cleaner later discovered.

During her trial, Sillanpää remained silent. Authorities could not find a clear motive for her actions. Mental health evaluations revealed that she had schizophrenia and a delusion about being the widow of an FBI agent. In court, the state prosecutor sought a prison sentence for manslaughter, arguing she had acted with premeditation. However, the district court found Sillanpää legally insane, ruling that she would not serve time in prison. This ruling was upheld on appeal.

Sillanpää was sent to the Niuvanniemi mental hospital for treatment. Following the incident, the Finnish Ministry of the Interior reviewed the security rules at shooting ranges. They made the participation requirements for first-time visitors stricter to enhance safety.