There are a total of 361 victims in the case, all boys aged between 9 and 15, with police saying they suspect the true number could be as high as 900.The defendant covered his face as he appeared via a video link from Kanta-Häme District Court. Image: Jarkko Vuolle / YleYle News7.9. 12:39Pirkanmaa District Court has begun proceedings in what is believed to be the largest-ever sexual crimes case in Finnish legal history.The hearings are expected to last until at least the end of this year, with the court sitting on 45 separate days throughout the coming autumn and into the winter.The schedule, announced in court as the first hearing began on Monday morning, reflects the vast number of victims in the case — 361. Police said there may be many more, even as high as 900, as some 530 potential victims have yet to be identified.The known victims are all boys aged between 9 and 15 years old, and they live in many different parts of Finland. Some legal representatives will participate in the session in court in Tampere, while others will join remotely from several different district courts.The defendant, a 28-year-old man, will appear before the court remotely from Kanta-Häme District Court. He is charged with aggravated sexual abuse of a child, sexual abuse of a child, and aggravated distribution of images depicting a child in an offensive manner.Man posed as a woman in Snapchat messagesThe crimes are alleged to have occurred on the Snapchat messaging app between 2019 and 2022.According to police, the defendant posed as a woman on Snapchat and sent messages to the children asking them for photos and videos. He then used screen recording software to capture the images without the knowledge of each sender.The number and content of the images and videos vary by victim, but one boy sent about 160 videos to the defendant.Police do not believe that the man met any of the children in person, meaning all the crimes occurred online.They do however suspect that he knew some of the victims beforehand, either through sports or while working as a substitute teacher.Attorney Jyri Kilpi, who is representing 77 victims, told the court in his opening statement on Monday that the defendant used the rosters of underage sports teams to select his victims and to understand more about their interests and hobbies.He described the shame and regret his clients, and their parents, feel as a result of the defendant's actions — noting that many could not bring themselves to tell their parents what had happened."All responsibility lies entirely with the adult perpetrator, not the victim," Kilpi said.Prior convictionAccording to Yle's information, the defendant in this case was sentenced to three years in prison in 2023 after being found guilty by Kanta-Häme District Court of the aggravated sexual abuse of a child.The court heard that the then-20-year-old defendant had sexual intercourse with his 14-year-old male student, while he was working as a substitute teacher at a primary school in the region. He also sent the boy hundreds of sexually suggestive messages, images, and videos.The investigation of this case led the police to confiscate the suspect's phone, where they subsequently found thousands of sexualised images and videos of children.