If the boy had simply stabbed a teacher over an iPhone, then okay, the additional information about his father and relative is at best unnecessary, at worst intentionally inflammatory.
Having read the article in #16, assuming it's the one Spinatwachtel also read, I think it's a lot less clear-cut than that, and that we do the journalist a disservice by suggesting his detail was deliberately tangential or inflammatory.
Firstly, paragraph 3 says:
"Bradford crown court heard that the attack was premeditated and partially racially motivated. [The victim] is black and the boy, who is of Pakistani origin, regularly referred to him “by the epithet beginning with the letter N”, the prosecuting barrister said. "
I don't think it's inappropriate for the journalist to mention race, given the circumstances of the attack. As for religion, paragraphs 4 & 5 read:
"[The victim,] a committed Christian, he said he was praying to God that the boy “would realise that violence is no path to take and that He would help him rather to become a useful member of society.”
"In the public gallery, the boy’s father, wearing a white tunic and crocheted skull cap, listened with his head bowed, while another relative fingered a string of prayer beads."
I don't think there's anything sinister or even negative in the journalist mentioning the prayer beads and skullcap. I think he's simply alluding to the unusual "religiosity" of the case, that there were two particularly religious parties in court.