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From the outset, police knew Kemarni Watson Darby's injuries could not have been the result of an accident.
The jury was told "Kemarni had been the subject of repeated and, in all probability, sustained assaults."
Around five hours after Kemarni’s mother made an emotional 999 call to the ambulance service, she had been arrested by police.
Her boyfriend at the time, who it’s claimed had just tried to save Kemarni’s life, was also arrested.
Alicia Watson and Nathanial Pope had met through mutual friends on social media and arranged to meet face-to-face after speaking on Facebook.
Pope told Birmingham Crown Court that at the time there was ‘no commitment’ to each other and they were free to see other people.
But they soon lived together at a flat Stanton House, Beaconview Road in West Bromwich.
Both denied murder and child cruelty, and in court the pair turned on each other.
During her evidence at Birmingham Crown Court, Watson said allegations that she murdered her child made her "sick".
When she was asked what she thought of Pope by her barrister Charles Sherrard QC, Watson said: "I hate him. He took away my child."
Mr Sherrard continued: "He says you did it. What do you say to that?"
Watson replied: "He is a cold-hearted liar."
Mr Sherrard said: "Did you have any reason to believe that Pope was doing anything to Kemarni?"
Watson replied: "No."
Mr Sherrard continued: "Do you accept that the injuries were caused by one of the two of you?"
Watson said: "Yes."
The barrister said: "Who then murdered Kemarni?"
As she sobbed in the witness box, Watson replied: "Pope did."
Watson told jurors she never suspected Pope was harming her son at the time.
When Pope took to the stand, the 32-year-old denied he "lost it" and beat the youngster to "shut him up".
He went on to say he had been "replaying events in his mind" but had not suffered any sleepless nights over Kemarni’s death.
During cross-examination, prosecutor Tony Badenoch QC put it to Pope: "You must be horrified by the realisation that you have been in a relationship with a child killer - a mother who killed her own three-year-old?"
Pope said: "Yes."
Mr Badenoch continued: "A child killer who has landed you in custody, accused of this dreadful crime. It's horrendous isn't it?"
Pope said: "Yes."
Mr Badenoch said: "You must have had many sleepless nights trying to piece together in your own mind what had happened?"
Pope said: "No."
Charles Sherrard QC, defending Watson, suggested Kemarni was 'moaning and whining' in the family's flat before he died.
The barrister put it to Pope that he was telling a 'pack of lies' and it was 'simply not possible' he heard no concerning noises from Kemarni - instead, suggesting the defendant hit the boy to the face.
Mr Sherrard said: "The blow to the face was, I suggest, designed entirely to shut him up?"Pope said: "I did not put any blows to his face."
Mr Sherrard continued: "And then it was you who followed it up by grabbing him by one arm, quite possibly lifting him up, so you could deliver blows to his belly, with such force it effectively went through to his spine."
Pope replied: "That never happened."
Mr Sherrard said: "Are you sitting there and honestly suggesting that it was Watson who did it to her baby boy?"
Pope said: "Yes."
It was claimed in court that both would use drugs, often inside the flat.
Pope told the court how he would travel to London to buy cannabis or see family.
He said Alicia also smoked cannabis but a different type called 'skunk', which he described as "much stronger than the homegrown Jamaican weed he would smoke".