A woman and her partner have been found guilty of murdering her 15-year-old son following a campaign of “utterly horrific and prolonged” torture. Sebastian Kalinowski died in hospital on 13 August 2021 of an infection caused by “untreated complications of multiple rib fractures”, following weeks of abuse and assaults by his mother, Agnieszka Kalinowska, 35, and her long-term partner, Andrzej Latoszewski, 38. The boy had arrived in the UK from Poland in October 2020 to live with the couple. Over the following months, the jury heard that the teenager was beaten repeatedly by them and subjected to cruel punishments if they thought he had misbehaved. A jury at Leeds crown court heard that Kalinowski was beaten with a bed slat, whipped with an extension cable and stabbed with a needle. Teaching staff had told the court he was “a pleasant and well-mannered boy” who “was observed to be quiet and timid, and at times appeared sad”. After the couple were arrested in connection with Sebastian’s death, police seized CCTV cameras from their house in Huddersfield, West Yorkshire, which prosecutors said had been partly used to “monitor and exert control over Sebastian remotely”. He was also verbally abused by the couple and ordered to address Latoszewski as “Mister” or “Sir”. The pair had denied murder and Agnieszka Kalinowska cried loudly in the dock when the verdicts were delivered on Friday after the jury had been deliberating for about three and a half hours. Latoszewski showed no emotion as he stared at the floor. The judge said they would not be sentenced until at least October and praised the jury, who had to watch the “horrifying” footage from the CCTV cameras multiple times during the trial. Mrs Justice Lambert told the jury: “You have had to endure quite horrifying footage of him suffering great pain over a long period of time.” The prosecutor, Jason Pitter QC, told the jury during the trial that the punishments Kalinowski faced were “by any stretch of the imagination cruel and became increasingly more severe and violent over time”. He added: “It would appear that the punishments were precipitated by things such as Sebastian merely dropping food on his bedroom floor, or even just having gone to the toilet during the night.” Pitter added that emergency services were called to the defendants’ house by Latoszewski on 13 August 2021 “after Sebastian had been unconscious for some two and a half hours”. The court heard that an examination of the boy revealed injuries including bruising to his buttocks, forehead, jaw, abdomen, arms and legs, and multiple rib fractures. After the verdicts, senior crown prosecutor Daniel Lee said: “Agnieszka Kalinowska and Andresz Latoszewski were the two people Sebastian should have been able to trust the most in the world but instead of loving, protecting and caring for Sebastian, they subjected him to an utterly horrific and prolonged campaign of extreme physical and mental abuse. In short, they tortured him. “Both defendants lied and offered cowardly and implausible explanations for the extent of Sebastian’s injuries, and attempted to pass it off as ‘appropriate discipline’. It is impossible to contemplate the agony and fear this young boy experienced, inflicted in his own home, by his supposed care-givers.”