Ther was no ecidence the boy didn't run off though. The prosecution is meant to prove guilt beyond reasonable doubt. I think boy b has grounds for an appeal.
Boy a I have zero sympathy for though.
Just to dig into this as it is a favourite topic of mine. IMO an appeal is difficult as the jury is the ultimate arbiter of factual questions, and appealing questions of fact is extremely difficult.
While it is true that the prosecution must prove guilt to BARD standard, this does not mean every fact of the case must be proved BARD. Instead the jury is to consider what facts it accepts and then draw logical and obvious inferences from the facts they believe were established.
Also while the defence does not need to prove innocence, from an evidential standpoint, he who asserts must prove. This means that if the defence wants to argue positively for a particular version, from a practical evidential perspective, they will need to point to facts which support it. And alibi is an obvious example of this. It's no good simply to claim an alibi. You need some facts to stand the alibi up. If you can point to some facts that establish your alibi - so there is a reasonable possibility your alibi is true, then as usual, the prosecution would need to disprove it or you must be found not guilty.
So how does all this impact the current case?
IMO the prosecution has significant evidence of a joint venture involving Boy B. The conversation at school. The tape. Luring Ana to the house. Evidence she was ambushed as she entered the room. Presence at the assault. Failing to help the victim. Covering up the murder.
Call me old fashioned, but this is easily enough to infer guilt to murder, even if Boy B didn't "pull the trigger". IIRC the state does not need to untangle the precise role of each participant. There is a public policy aspect to this. You can't go getting involved in pre-meditated violent assaults like this, then go crying that someone went too far. At the very least, an accused would require hard evidence that he ended his involvement.
So in the present case, Boy B's defence argues for a positive version. The two key elements appear to be that he did not know Boy A planned to attack Ana, and that he ran away when things got very violent.
Let's make one point here. Boy B did not set out his version in testimony at trial (as his right). Argument for a version by counsel is also not evidence. So in fact the only evidence before the jury on these 2 key points are the interviews of Boy B
So how should a jury evaluate this version?
A jury assesses both the veracity and credibility of a witness. Boy B obviously has little credibility as a witness due to his repeated lying. There is no reason for the jury to think he is telling the truth. Legally, a jury is fully entitled to disregard the evidence of Boy B as unreliable, except where veracity is otherwise established.
This is the approach i would have taken. Boy B's evidence goes in the dustbin, apart from where he was forced to make key admissions by the pressure of external evidence (witnesses, CTV)
So if I was a juror I would have made 2 factual findings adverse to Boy B
1. Boy B most likely lured Ana to the house for the purposes of a sexual assault. His claim that it was so Boy A could talk to Ana is clearly a lie IMO. He provided the tape. This was premeditated.
2. He was most likely present for the entire attack.
tldr;
the jury did not believe Boy B, and instead made more logical inferences from the evidence
Last step
Standing back - is the case against Boy B proved BARD? IMO yes. Lots of evidence points to his joint involvement, and he has no credible defence.