But where is the info coming from that his mother would be doing such a thing? I'm asking for source material.
I haven't found anything in the Ward & Patterson book which implies they are speaking.
I haven't done the Howard Blum book but in his most recent interviews, everything he says about BK's family's thoughts seems to be third hand so I don't think they're talking to any reporters/authors on background, which is understandable considering hideousness of the crime & coming to terms with reality that your own child is the perp.
Blum ( Dateline) speculated BK's father might have suspected on the car trip back to PA. ( Speculation which is of no greater weight than what we do here. I'm minded to think it was maybe the sisters who suspected most, as we heard originally. )
Blum also claimed that the family, particularly the mother, prompted BK to admit his guilt after seeing Dateline but this was also third-hand info.
OTOH I do think it's plausible that the family were shocked at the Dateline contents ( especially the new revelations such as internet searches wrt rape, trying to find a new knife & sheath etc.) It wouldn't surprise me that prior to Dateline, he'd been adamant about his innocence to them. ( There are a lot of examples in the Ward-Patterson book where BK is furiously denying the undeniable to a range of people, through his teen years. )
Anyway, maybe Dateline streams, then the scales fell away for the parents. ( In their position I'd probably threaten my son that I'd abandon him if he didn't admit his guilt. That would also mean no funds & no prison comms until he did which might focus his mind)
Nonetheless, if Blum is right, it would be ironic if breaking a gag order - to produce media sensation pre-trial - was the straw that broke the camel's back & prevented the trial taking place.