A mother accused of torturing her son to death alongside her partner sobbed as she told a court she “should have died instead of him”.

Sebastian Kalinowski died last August of an infection caused by “untreated complications of multiple rib fractures”, which prosecutors say came after weeks of “cruel assaults and abuse” at the hands of his mother and stepfather.

Jurors at Leeds Crown Court have heard the 15-year-old boy was beaten with a bed slat, whipped with an extension cable and forced to perform “humiliating” exercise drills in what prosecutors say amounted to a campaign of “torture”.

At the time of his death, Sebastian had been in the UK for less than a year after moving from Poland to live with his mother Agnieszka Kalinowska, 36, and her partner Andrzej Latoszewski.

Prosecutors say the abuse by the couple was captured on CCTV cameras they had installed to “monitor Sebastian remotely” at their house in Huddersfield, West Yorkshire.

Jurors have heard the footage, seized from the house after Sebastian’s death, shows him “being attacked, principally and most severely by Latoszewski but with his mother being involved at various times”.

The prosecution’s case is that both defendants are guilty of murder because “both of them acted together to inflict the fatal injuries on Sebastian as a course of conduct”.

On Wednesday Kalinowska told the court she was “petrified and scared” of Latoszewski, and that it was a “controlling relationship”.

Kalinowska and Latoszewski both deny murdering Sebastian.

Latoszewski, 36, admitted manslaughter on the second day of the trial, while both defendants pleaded guilty to child cruelty a day later.

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

Speaking through a Polish interpreter, Kalinowska told the court she admitted being cruel to Sebastian, but had not pleaded guilty to manslaughter because she did not cause any of his rib injuries, nor did she help or want Latoszewski to break her son’s ribs.

Asked by her barrister Leonard Smith QC why she was cruel to Sebastian, Kalinowska said: “Because I listened to Andrzej’s words.”

Asked why she watched her partner “inflict the most savage beatings on your own son” without intervening, she replied: “Because I was petrified and scared.”

When Mr Smith said she was thinking of herself instead of her son, she said: “Yes. He was just an ordinary teenager. I failed as a mother. I should have died instead of him.”

She described Sebastian as a “good child” and said Latoszewski’s claims to his school that he was “naughty and lying” were not true.

Asked whose decision it was to start punishing Sebastian, she said: “Andrzej’s, because he was the head of the house and he was deciding everything.”

The court was shown one CCTV clip of Kalinowska kicking out at Sebastian as Latoszewski beat him.

She said: “Andrzej told me to do something. He said I was just standing there and as his mother I should have intervened.”

Asked why she was using her weight on Sebastian’s leg during another clip of him being assaulted by Latoszewski, Kalinowska replied: “Because Andrzej told me to, he told me to hold Sebastian and because I was petrified I was just doing what Andrzej told me to do.”

Kalinowska admitted calling Sebastian “foul and disgusting names”, saying it was “because I was used to those words, because those were the words Andrzej used to address me, so that type of language was being used in the house.”

Asked about a recording of her shouting at Sebastian, she said Latoszewski had installed an app to “record every single conversation on my phone” and she “wanted Andrzej to know I was disciplining Sebastian in the way he expected me to do”.

As Sebastian’s punishments became more severe, Mr Smith asked, “Did you ever think, this has gone too far, I have to save my child?”

Kalinowska was tearful as she replied, “No.”

The court heard Kalinowska had Sebastian when she was 19 years old, and that he had lived with her until the age of four, when she moved to the UK “to earn money to improve Sebastian’s life”.

Sebastian then went to live with his biological father, it was said.

Kalinowska said she met Latoszewski through friends and he offered her “this better life in the UK”.

She told the court they started a relationship after she moved to England, but that it was “not a good relationship,” and that Latoszewski started “controlling me and then beating me up” after around two years.

Kalinowska said she brought Sebastian to the UK in 2020 “because I wanted him with me”.

The trial continues.