"Evil" teen Craig Mulligan appeared emotionless as he was quizzed by police days after murdering Logan Mwangi.
The babyfaced killer was named for the first time today after he was convicted of the five-year-old's murder alongside sick stepfather John Cole, 40, and stepmother Angharad Williamson, 31.
Mulligan, the son of Cole's ex-partner, had previously been under the care of foster parents who described him as 'pure evil".
Footage released by South Wales Police ahead of an ITV documentary on the horrific killing shows Mulligan in a prison-issued tracksuit as he seems calm and unbothered by police questions.
Throughout the interview, Mulligan maintains he did not know what happened to Logan, claiming he had woken to hear the child's mum shouting 'Logan is dead'.
Police are then heard telling Mulligan that Williamson had blamed him and Cole for Logan's death, before he retorts with: "You can tell my mum to f*** off for me. She's blaming me and my dad for everything."
During the trial the teenager's identity remained anonymous due to his age, before judge lifted the reporting restriction after he was jailed for 15 years.
Williamson was jailed for 28 years and Logan's stepfather Cole was jailed for 29.
Logan's body was dumped in a river in Bridgend, South Wales, with the child having suffered catastrophic internal injuries akin to a high-speed car crash.
His remains - found on the morning of July 31, 2021 in the River Ogmore near Pandy Park - also bore more than 50 external wounds.
Williamson collapsed to the floor as the verdict was delivered, saying "no, no, no, no, no", then shouted at Cole: "You lying motherf****** murderer, you lying murderer.”
She silently wept as she was jailed for life.
The judge said, referring to Logan: "He was five years old and was described by everyone who knew him as a wonderful child.
"Bright, chatty and artistic. A little boy who could light up a room. There is no word for his death other than it was a tragedy."
She went on to say: “Because he was killed in his own home it’s not possible to be sure exactly what happened to him.
"What is very clear is shortly before his death this little boy was subjected to a brutal attack.
“There were 50 external injuries on his body, a blunt force trauma injury to his head, another non-fatal injury caused 36 hours before his death.
"Elsewhere on his body were injuries consistent with three to four punches to the abdomen and kicks to the rear.
“He suffered substantial internal bleeding. There was a tear to the lower part of the lobe of the liver, a 5cm tear to the right of the small bowel, the duodenum had been torn from the pancreas, and there was a degloving injury to the duodenum.
"These are the sort of injuries caused by a high-velocity impact or a fall from 10ft but they are consistent with the sort of injuries seen in abused children.”
She said the injuries were indicative of a severe localised blunt force caused by a weapon or object.
The judge added: “To see these injuries on a small, defenceless five-year-old is nothing short of horrifying.”
In a victim statement read out on behalf of Logan's distraught dad Ben Mwangi, he described having "vivid" recurring nightmares about failing to save his son - having been banned from seeing him by Cole.
"He runs into my arms and I hold him tight but he then slowly disappears until he's no longer in my arms," he said in the statement, read by prosecutor Caroline Rees QC.
"I wake up screaming and crying. I find it difficult to go back to sleep. I don't want to go back to sleep because I don't want to experience these dreams because they are so painful."
Mrs Justice Jefford said in response: “The effect on Ben Mwangi and his family has been devastating.”
Ms Rees also told the court that, despite Logan's horrific injuries, if medical assistance had been sought, he "would have had an 80% chance of survival".
She said in the months and weeks leading up to his death, Logan had been "dehumanised" by his family.
Logan's stammer is said to have worsened, becoming particularly bad around Cole. He wet himself more frequently and began self-harming.
Friends of the couple said Cole told them he did not like Logan.
After Williamson gave birth to his own child, Cole was reluctant to let Logan see the baby and later claimed the boy had tried to smother the infant.
Jurors had watched chilling CCTV footage of Cole and the youth carrying Logan's body out of the family home.
The grainy video captured at 2.43am on the same day the remains were found by police the pair can be seen leaving Williamson's flat, with the dead child's arm dangling across his evil stepdad's back.
Williamson herself made a dramatic 999 call at 5.46am to report her son missing.
Later, when police came to reveal Logan had been found and taken to hospital, the killer mum cried crocodile tears during a theatrical display.
But, captured on the officers' bodycam, she perhaps tellingly muttered: "This is all my fault."
