Kristy Bamu, 15, was killed after what a prosecutor described as "a staggering act of depravity and cruelty."
LONDON -- A British jury on Thursday found a couple guilty of torturing and murdering a 15-year-old boy whom they accused of witchcraft.
Magalie Bamu and her partner Eric Bikubi, originally from Congo, were convicted of killing Magalie's brother Kristy Bamu, who drowned in a bathtub on Christmas Day 2010.
Bikubi, 28, and Magalie Bamu, 29, had pleaded not guilty.
Prosecutors at London's Central Criminal Court said the teenager had 130 injuries inflicted by sticks, a metal bar, a hammer and a chisel. They said he eventually drowned after being forced into a bathtub and doused with cold water.
The court heard that Kristy was in such pain after days of violence that he "begged to die" before drowning, the BBC reported.
The boy "had been the victim of a prolonged attack of unspeakable savagery and brutality," prosecutor Brian Altman told the jury.
Kristy's sister and her boyfriend beat him as part of a "deliverance" ceremony because they believed he had cast spells on another child in the family, according to the prosecution.
Kristy and four siblings aged 11 to 22 lived in Paris but had been visiting their older sister in London for the holidays. Soon after they arrived, Bikubi accused them of bringing witchcraft into the home.
All were forced to pray for deliverance for three days and nights and deprived of food and water. Two sisters, aged 20 and 11, were beaten along with Kristy, but escaped further attacks after "confessing" to being witches, the prosecution said.
The family of the victim said they had "forgiven" his killers, the BBC reported.
"We will never forget, but to put our lives back into sync we must forgive," the family said in a statement read out by their lawyer in court. "We take no comfort in the verdicts -- we have been robbed of a beloved son, a daughter, a son-in-law."
"Kristy died in unimaginable circumstances at the hands of people who he loved and trusted. People who we all loved and trusted," the statement continued, according to the BBC.
Judge David Paget, presiding over his last trial before retiring, said the case was so "harrowing" that every member of 12-person jury was exempted from jury service for the rest of their lives.
Bikubi and Magalie Bamu will be sentenced Monday.
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Msnbc.com staff and The Associated Press contributed to this report.