A couple whose three-year-old son was found buried in a garden after they opted out of society and set up their own “kingdom” have been convicted of causing or allowing his death through “breathtaking” neglect.

Jurors unanimously convicted Tai and Naiyahmi Yasharahyalah after hearing how they kept the body of Abiyah Yasharahyalah in their bed for eight days after he died from a respiratory illness, worsened by a “restricted” vegan diet which caused severe malnourishment, rickets, anaemia and stunted growth.

The couple then “embalmed” and buried the toddler in an 80cm-deep grave at the rear of their then-home in Clarence Road, Handsworth, Birmingham, at the start of the Covid pandemic in early 2020.

A two-month trial was told London-born Tai, a medical genetics graduate who also used the first name Tai-Zamarai, and former shop worker Naiyahmi shunned mainstream society and were eventually arrested in December 2022 while living in a caravan in Somerset.

A post-mortem on Abiyah’s “skeletal” remains and other tests failed to identify how he died, but suggested he was also suffering from severe dental decay and six fractures to his right arm, legs and ribs, possibly caused by a fall around six weeks before his death.

Jurors deliberated for more than 21 hours over five days before unanimously convicting the couple of neglect, perverting the course of justice and causing or allowing death.

The verdicts, delivered on Thursday, came after jurors heard that Abiyah was neglected by being given inadequate food and through a failure to summon any medical treatment as he battled a fatal respiratory illness.

The trial was told that police visited the Clarence Road property three times – in February 2018 when Abiyah was alive, again in September 2021 after his death, and then in March 2022 to assist in the couple’s eviction for non-payment of rent.

On the second occasion, police bodycam footage recorded officers asking if a child lived at the address and Tai becoming aggressive and being arrested for being obstructive.

The welfare check did not lead to Abiyah being identified as missing, due to confusion over records related to the address.

A child safeguarding practice review is ongoing into Abiyah’s death, examining police and other agencies’ involvement with him during his life.

The trial was told that instead of contacting the NHS, the couple – who told police they had renounced British citizenship and had an “off-grid” existence – tried to treat their son’s final illness with garlic and ginger.

The couple were both “extremely thin” when they were arrested on December 9 2022, leading to the discovery of their son’s body five days later.

Tai and his 43-year-old wife, who was born in Birmingham to a Christian family, denied the charges against them, telling the court they did not act wilfully and believed Abiyah would recover from a flu-like condition.

Former fitness instructor Tai, aged 42, told police in interview that he had carried out an “eight-day ritual” hoping that Abiyah would “come back”, but had eventually decided to conduct a burial in accordance with his culture on what he regarded as sacred ground.

He told jurors he had adopted polygamy but had rejected being an omnivore as part of his quasi-religious “kingdom” – but accepted that he had been “foolish” in following his own legal doctrine.

Although he had studied immunology and how diseases affect genes before graduating from Queen Mary University of London, Tai claimed he was unaware of the risks of a strict unsupplemented vegan diet.

Jurors heard that the couple met in the street while Tai, who moved to Birmingham in 2014, was busking and introduced himself to his future wife, whose original name was Donna Graham as the “King” of the Kingdom of Yasharahyalah.

The couple got married at a register office in September 2015 and “invented” a belief system featuring aspects of Igbo culture that Tai, who grew up in both Nigeria and Peckham in south-east London, adapted to form a legal system he called “slick law”.

The court heard that they lived off the generosity of others, occupying a shipping container and then a caravan in the Somerset area.

Post-mortem tests failed to ascertain the cause of Abiyah’s death because tests on soft tissue, which had decomposed, could not be carried out.

But experts were able to say that if the three-year-old died from a respiratory illness, as described by his parents, the effects of malnutrition would have been a “more than minimal” cause of his death.

Police body-cam footage of the couple being removed from the caravan amid welfare concerns was also viewed by the jury, with Tai screaming at police about back problems and Naiyahmi appearing to read from a computer screen as she said: “Leave my personal private space, I am an indigenous person.”

After they were taken to hospital, Abiyah was spotted on social media posts recorded by Tai and when asked where the boy was, the couple admitted they had buried him and failed to register his death.

Opening the case for the Crown at the start of the trial, prosecutor Jonas Hankin KC claimed the couple had jointly neglected Abiyah by failing to provide him with enough food or any medical help.

Prosecutors alleged it would have been obvious to both defendants that Abiyah, whose teeth would have been wobbly, was in considerable pain from abscesses and other ailments.

Mr Hankin said: “This child started life small but normal, and over time he became abnormally small. Those features must have been discernible to his parents if, as they claim, they were caring, loving and attentive.”

Referring to a comment made by Abiyah’s mother that “nature has a way of doing things”, Mr Hankin added: “That is their attitude ‘We’re right and nature will decide’.”

“It is breathtaking arrogance and cruelty,” he added.

The couple’s lawyers argued that the couple had buried Abiyah in the hope he might be “born again” and not in order to hide the death from the authorities.

Defence lawyer Bernard Tetlow KC told the trial: “Tai and Naiyahmi were not saying to themselves we realise our diet, we realise our healthcare is bad for us, but we are going to do it anyway.

“They genuinely believed they were doing the right thing. They genuinely believed that their diet and the belief in natural and holistic medicines was the best way.”

Commenting after the verdicts, Detective Inspector Joe Davenport, the senior investigating officer, said of Abiyah’s father: “I would describe him as a very arrogant man, a fantasist, and someone who looked to manipulate people.

“And I would say that Naiyahmi, as his one and only follower, was incredibly weak-minded to put her love of Tai-Zamarai ahead of the needs of her own child and the need to please him ahead of the welfare of Abiyah.”

The couple, who were on bail during their trial, were remanded in custody and will be sentenced next Thursday at the same court.