A man accused of torturing and murdering his long-time partner's 15-year-old son, Sebastian Kalinowski, has pleaded guilty to manslaughter.

Andrzej Latoszewski and the boy's mother, Agnieszka Kalinowska, have been accused of murdering the teenage boy at their house in Huddersfield, West Yorkshire in August 2021. Latoszewski, however, denies murder even after admitting to manslaughter.

During a hearing of the case in Leeds Crown Court, the prosecutors said that the duo tortured the boy for weeks before he finally died due to untreated rib fractures which caused an infection, per a BBC report.

Prosecutor Jason Pitter QC told the jury the boy had come to live with his mother in the UK from Poland in October 2020, and that initially Kalinowska was thrilled to be with her son. But things took a turn for the worse.

A friend of the woman told the court that the couple had started to see the boy as a "hindrance," by the end of 2020, and started punishing him for "minor wrongs." These "became increasingly more severe and violent over time," he said.

Sebastian Kalinowski was "kept deliberately out of the way of others, either as part of the system of punishment or to hide the abuse."

"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," he told the jurors.

The CCTV footage accessed by the police showed the teenager being beaten with a slat from a bed, abusing him, and whipping him with a cable at one instance. Latoszewski was seen "forcing food and drink into Sebastian's mouth" and "stabbing him a number of times" with a needle in the groin and thigh on the day before his death, according to prosecutors.

Pitter further stated that it was not just Latoszewski who tortured the boy, but the mother would also join him. At one point she also "took over stabbing Sebastian with the needle." He was assaulted on the day of his murder as well.

The CCTV footage showed him lying unconscious on the floor. However, the couple allege that they found him unconscious in the bathtub. The trial in the case is still ongoing.

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Crime scene police line | Representational Image Photo: GETTY IMAGES / SCOTT OLSON