Olavi Karhu was a prisoner held at Köyliön varavankila, a Finnish auxiliary prison located in Köyliö that operated between 1935 and 1998. At the time of the incident, Karhu was serving a prison sentence and had documented mental health issues; he was known to threaten suicide on numerous occasions. Prison staff had repeatedly confiscated items that Karhu had obtained with the intent to harm himself.

At the time of the arson incident in 1959, Karhu was reportedly awaiting transfer to a detention hospital (vankimielisairaala) in Turku due to these issues. 

On the night of 1 July 1959, at approximately 22:30, an arson attack was deliberately initiated in the Länsiosasto (West Wing) of Köyliön varavankila, a Finnish prison facility. The fire was started by Olavi Karhu, who had placed a straw mattress and clothing against the door of his solitary cell and lit them. When a guard opened the door, the flaming mattress fell into the corridor, rapidly turning the wooden prison barracks into an inferno.

The West Wing was constructed largely of untreated timber with turvepehku (peat bedding) and sawdust insulation, materials that provided extremely poor fire resistance. Once the fire began, it spread quickly throughout the barrack. Prisoners housed in the structurepredominantly minor offenders such as car thieves, shoplifters, and drunk drivers were trapped inside.

At the time of the incident, the wing housed between 62 and 90 inmates, depending on the source. Despite the efforts of up to 25 local fire crews, the fire raged out of control. Prisoners were released from their cells and assisted in firefighting, but many sections were gutted before help could reach them.

A significant rescue effort followed, involving police and military support. It took until about midday the following day to locate the remains of the victims. In total, 16 prisoners were killed in the fire. They were all serving sentences of under five years; the oldest was born in 1927 and the youngest was 18. Two of the victims were scheduled for release the next day. At least some inmates trapped inside managed to reach hospital with severe burns.

Surviving prisoners reported that one inmate, acting with strength and determination, aided several others through a window escape route but became fatally trapped himself.

The fire exposed critical deficiencies in the design and safety of the prison’s wooden barracks. Parake structures had walls composed of wooden boards filled with highly combustible materials, and a central firebreak door had been left open when the fire began allowing the blaze to spread unchecked.

Following the fire, authorities initiated an investigation and trial in October 1960 at the Kokemäki District Court. The prosecution argued that prison guards had contributed to the severity of the fire by leaving a critical door open, facilitating the spread of the blaze. The court ultimately acquitted the guards of criminal liability.

However, the court held Olavi Karhu’s parents financially responsible for damages to the state, ordering them to pay 15 million Finnish markka to the government and 300,000 markka to other claimants from Karhu’s estate. The ruling prompted debate and public scrutiny, with questions raised in the Finnish Parliament. The Turku Court of Appeal and the Supreme Court upheld the financial liability decision, although practical enforcement against the parents was limited under clarified legal interpretation.

In the wake of the fire, prison authorities acknowledged serious safety failings at Köyliön varavankila. Rebuilding efforts commenced, and by the mid‑1960s, the destroyed West Wing was replaced with modernized facilities. Over subsequent decades, the prison underwent further improvements, with new accommodation blocks, infrastructure upgrades, and industrial workshops established.