Eric Bikubi and Magalie Bamu are found guilty of murdering 15-year-old Kristy Bamu, Magalie's brother, whom they accused of witchcraft, on Christmas Day 2010.

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Kristy, aged 15, was tortured repeatedly and was eventually drowned in the bath by his sister and her partner.

The Old Bailey heard that the couple believed he had cast spells on another child in the family and believed he had to be punished.

Football coach Bikubi, 28, and Bamu, 29, of Newham, east London, denied charges of murder but were found guilty. They were remanded in custody and will be sentenced on Monday.

Bamu was found guilty by a 10-2 majority verdict.

Judge David Paget told the jury that the case was so "harrowing" that he would exempt them from jury service for the rest of their lives.

"It is a case we will all remember," he told them. "Court staff will speak to you and offer help to you."

Kristy's family were not at the court, but his father, Pierre, read a public statement: "Kristy died in unimaginable circumstances at the hands of people he loved and trusted, people we all loved and trusted. I feel betrayed. How could they accuse, judge and sentence?

"To know that Kristy's own sister, Magalie, did nothing to save him makes the pain that much worse."

'Begged to die'

Over three days, Kristy was attacked with knives, sticks, metal bars and a hammer and chisel, at the hands of his sister and her husband. He was in such pain that he "begged to die" before being submerged under water in the bathroom.

Kristy asked for forgiveness. He asked again and again. Magalie did absolutely nothing. She didn't give a damn. She said we deserved it. Kelly Bamu, sister

Kristy and his other siblings visited their sister Magalie and her husband over the Christmas holidays, leaving their parents behind in Paris.

Bikubi had turned on the youngsters shortly after they arrived, accusing them of bringing kindoki - or voodoo - into his home.

He forced them to pray for "deliverance" for three days and nights and deprived them of food and water.

The sisters, aged 20 and 11, were also beaten, but they escaped further attacks after "confessing" to being witches. Kristy refused to admit to sorcery and witchcraft and his punishment became more severe. Kristy's final words to his father were "Eric will kill me."

He had been singled out after wetting his pants, and was struck in the mouth with a heavy bar and hammer, knocking out his teeth. Ceramic floor tiles and bottles were smashed on his head and his ear was twisted with a pair of pliers.

The court heard that Kristy's siblings, who also included a 13-year-old boy and an autistic brother aged 22, were made to join in the torture. At one point Bikubi told the youngsters to jump out the window to see if they could fly.

Their sister Magalie encouraged her partner and joined in the beatings.

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'Obsessed' with witchcraft

Kelly Bamu, now 21, broke down in the court room as she recalled the sequence of events.

"It was as if they were obsessed by witchcraft and then it became absolutely unbearable," she said. "They asked if we were witches. I repeated again and again and again that we were not witches.

"I did not know what was going on in their minds. They decided we had come there to kill them."

Kelly added: "Kristy [pictured] asked for forgiveness. He asked again and again. Magalie did absolutely nothing. She didn't give a damn. She said we deserved it."

Calling Magalie "an idiot", Kelly said: "I am sure she still believes even to this day that we are witches. I have no pity for her. She had no pity for us."

Kristy had 130 separate injuries and died from a combination of being beaten and drowning.

Paramedics who arrived at the eighth-floor flat tried to save Kristy but he was already dead. Police found Kristy's brothers and sisters in the blood-stained living room.

An 'under-reported' crime

Detective Superintendent Terry Sharpe said that the Metroplitan police had carried out extensive work to understand and tackle "belief-based child abuse", which includes witchcraft and spirit possession.

"However, this is a hidden and under-reported crime and therefore difficult to deal with in terms of protecting potential victims from harm," he added.

The NSPCC warned that Kristy Bamu's ordeal was not an isolated case. "The vast majority of people in the communities where it can take place are horrified by these acts and take no part in this atrocious behaviour," said the children's based charity.

"So we must not be afraid to challenge these communities to out the wrong-doers within them. But sadly this deeply disturbing case is not a one-off incident."