I'm not sure what you were alluding to but the first thing that comes to mind for me, is abuse.
He wouldn't be the first kid to do this, if that's what was going on.
Obviously this hasn't been stated yet, but it's one heck of a powerful motive for sure.
jmo
I was thinking of abuse, as well as asking myself what might have transpired between the divorce and the current husband. Is that possible that abuse might have happened in the hands of another guy and that mom was unaware? There might be displaced anger towards the mom who didn’t protect her son, or so so he thought.
Also, on a more practical note. How large was the apartment where the new lived and how close was the kid’s bedroom to his mom and her partner’s one? The boy is thirteen, puberty, he is starting to process something plus here is a new child, mom breastfeeding. I think it could have been simple Oedipal complex, maybe a normal phase of development, but the boy had no one to talk about it.
I, too, didn’t feel good about the pregnancy photo. In itself, there is nothing wrong in it except for it is pretentious and poorly executed. Just because a photographer chooses Annie Leibovitz theme, it doesn’t turn them into Annie Leibovitz. (In short: they chose a bad professional photographer. JMO). But for the boy already struggling with own puberty, especially if he was lonely. it might have been impossible to process own developing feelings towards women. He attacked mom because he was young and confused and no one noticed it.
My opinion: he should not be tried as an adult, no way.
He needs a counselor, now, he is at a huge risk of self-harm. He might be struggling from some mental condition plus having alexithymia and it contributed. It was realistically impossible for him to process all.
Probably just underscores the need for children of divorce to go through therapy. What could have been a phase of human development turned into a tragedy.
They might be Roman Catholics. Did the kid ever talk to a priest before it happened?
My condolences for Irina’s family. She left a very young baby and this boy. What a tragedy.