A teenager who is among three people accused of murdering a five-year-old boy had a “desire for violence” and threatened to kill the child and members of his foster family, a jury has been told. The 14-year-old boy, who cannot be identified for legal reasons, also used to “poke, pinch and kick” his social worker and would swear violently at her to try to aggravate her, the court heard. Logan Mwangi was found in the River Ogmore in south Wales on 31 July last year having suffered more than 50 injuries to his face, head and body. His mother, Angharad Williamson, 30, stepfather John Cole, 40, and the 14-year-old are on trial for his murder. In statements read to Cardiff crown court on Monday, members of a former foster family of the teenager claimed he made their lives “hell” when he lived with them in the months before Logan’s death. They claimed they had told his social worker that he had threatened Logan and them but she had brushed this off, an allegation she denies. The boy’s foster mother said she became concerned about what she called the teenager’s “desire for violence”, and said he wanted to spar with every person he met. She described his behaviour at one point as being like a “monster”. He allegedly told members of the family he wanted to kill them and said that if the plot of the film The Purge, which tells the story of a fictional holiday when all crime is allowed, was real, he would carry out his threat. The foster father said he became “terrified” of the youth, who had told him he wanted to “punch his lights out” and would walk around chanting about how he wanted to kill people. According to the family, the youth also tormented their dog, pulling him up by his hind legs and keep him dangling even though he was aware the pet had an injured pelvis. On one occasion he sprayed a can of deodorant into the dog’s eyes, the jury was told. The court heard how the teenager allegedly said he wanted to kill Logan. The foster family said they raised concerns about his behaviour and threats with his social worker Debbie Williams but they claimed she dismissed what they said as “nonsense”. “She just brushed it off as if it was nothing,” the foster mother said in her statement. Williams, giving evidence on Monday, broke down in tears when she described Logan as a “delightful little boy.” She said: “He was a happy boy. Bright eyes. He was very polite.” The social worker said that not long before Logan’s body was found she saw the teenager and he told her to “fuck off”. Williams said: “He told me to fuck off lots of times, it was more banter though sometimes he would go too far”. He had once called her a “cunt” and used to “poke, pinch and kick” her but she said he had never hurt her. Asked if the foster family told her that the youth had threatened to kill them and Logan, she said: “Absolutely not.” Williamson and the youth deny committing murder and perverting the course of justice. Cole denies murder but admits perverting the course of justice. The trial continues.