I think FM will get C/AD by having lived there and knowingly ignored (at the very least) what was happening.
The DNA on his own items won’t help him.
I do wonder what evidence has been brought in court but not reported - family court details, any additional phone records or work records, etc
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I can’t get past the eldest boy having messaged a friend to say Sara had died. What on earth did he think had happened, did he think she was unwell, was he conditioned to think she ‘deserved’ the ‘punishment’, or was he telling someone because he hoped they/parents could help.