The Bodom lake triple killing is one of Finland's most notorious unsolved murder mysteries.
The trial of Nils Gustafsson, which opened Thursday more than 45 years after the murders, is without precedent in Finnish legal history, and is expected to be a long and complicated process.
In the summer of 1960, two 18-year-old boys and two 15-year-old girls went camping on the shores of Lake Bodom, half an hour's drive from Helsinki. During the night, they were attacked.
Gustafsson insists that an outsider injured him and killed the other three campers.
"Strong New Forensic Evidence"
Prosecutors said Thursday that technical tests prove Gustafsson slashed open the tent from the outside before stabbing and beating his companions.
According to investigators, the evening at the lake was all about jealousy, alcohol and sex. They claim that Gustafsson, the sole survivor, lost his temper because of an old relationship of his girlfriend, who was stabbed in an extremely brutal manner, unlike the other two.
At the time, there was insufficient evidence to bring a prosecution. The prosecutors say they now have strong new forensic evidence.
The material going to the prosecution includes 500 pages of interviews and interrogation material, DNA and blood samples, fingerprints and other items.
Prosecutors plan to reconstruct the tent in the courtroom and exhibit key evidence including Gustafsson's shoes. The trial is expected to last about five weeks.
Now 62, Gustafsson will not appear in court for a couple of weeks. He has remained free while awaiting trial despite being accused of such a serious crime.