Lol, are you really doing this?
This kid went to British schools, he would've had a British education, British peers. His parents are Christian, been a long time since Christians have recommended killing others so your point irrelevant. Their son never witnessed anything in Africa growing up because he was raised in the UK and believe it or not, it's not in his DNA. His parents had got him help in his earlier years for mental health issues but didn't report him when they witnessed the violence getting worse because they didn't want him to be in care, as well as sounding like they were scared of him. Other issues are also at play. It's much more complicated than him having parents from overseas.
I was born overseas to British parents, lived in 3 Middle Eastern countries, and another European one before coming to Britain (or home as it was for the rest of the British born family). I went to local schools, played with local kids at school and in my neighbourhood and knew their parents. They cannot but be part of growing up and influence. The parents are not the only source of information a child grows up with abroad, I know.