A mother and her boyfriend have been found guilty of murdering her 15-year-old son who died after a campaign of torture at his home in Huddersfield.

Sebastian Kalinowski died of an infection caused by “untreated complications of multiple rib fractures” after weeks of “cruel assaults and abuse”, prosecutors said.

Sebastian was beaten with a bed slat, whipped with an extension cable and stabbed with a needle by his mother Agnieszka Kalinowska, 35, and her partner Andrzej Latoszewski, 38, a jury heard.

The boy, who moved to Poland to live with his mother in the UK less than a year before he died in August 2021, was also forced to complete “humiliating” exercise drills.

Kalinowska and Latoszewki also shouted derogatory insults at Sebastian in an effort to control and humiliate him.

Latoszewski, a body-builder involved in martial arts, insisted Sebastian address him as “Mr” or “sir”.

Kalinowska sobbed loudly in the dock after she was found guilty of her son’s murder.

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Police had seized CCTV cameras from Kalinowska and Latoszewski’s home after they were arrested in connection with Sebastian’s death.

Prosecutors said the cameras had been installed partly to “monitor and exert control over Sebastian remotely”.

The seized footage showed the boy being attacked most severely by Latoszewski but his mother was “involved at various times”, jurors heard.

CCTV footage from the day of Sebastian’s death showed Latoszewski taking him out of his bedroom at 8.25am before carrying him back 15 minutes later “naked, clearly wet and unconscious” and attempting to resuscitate him.

The emergency services were only called after Sebastian had been unconscious for around two and half hours.

The boy succumbed to an infection caused by “untreated complications of multiple rib fractures”.

Kalinowska and Latoszewski denied murdering Sebastian but were found guilty at Leeds Crown Court today.

Latoszewski had admitted manslaughter on the second day of the trial, while both defendants pleaded guilty to child cruelty a day later.

Kalinowska also denied causing or allowing the death of a child.

Prosecutors claimed both acted together to inflict fatal injuries.

The judge, Mrs Justice Lambert, said the pair will not be sentenced until October at the earliest.

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An NSPCC spokesperson said: “In the months before they brutally cut his life short, Sebastian Kalinowski’s mother and her partner – the very people who should have been nurturing him into adulthood – subjected him to cruelty and misery.

“People will be asking how any child in our society could suffer such an appalling campaign of abuse without anyone intervening.

“That is why it is so important that no stone is left unturned in the review looking into the circumstances around his death. We would urge anyone who is worried about the safety of a child or young person to speak out and seek support whenever they have a concern.”