IANAL, but I gather from reporting that this is what happened:
The defense
requested a plea offer from the prosecution. After consulting with the families (basically just telling them what they planned to do), the prosecution created a plea offer, and then the defense accepted it. (I imagine this process involved quite a bit of negotiation between the two sides to seal the deal.)
Next, AT and BT informed Judge Hippler on Monday afternoon about the plea offer so he could schedule the hearing ASAP. (I suppose they also told the families that BK agreed to the plea offer.)
Judge Hippler’s role during Wednesday’s hearing was to make sure the plea offer (or plea agreement) was sound—that BK understood exactly
what he was pleading guilty to and the ramifications of pleading guilty, and that BK wasn’t being compelled to accept the plea offer.
During the sentencing hearing on July 23/24, Judge Hippler will hear victim impact statements and determine whether or not to impose the maximum sentence included in the signed
Plea Agreement (which I just now noticed was signed on Monday, June 30, the same day Hippler was informed about it, and two days before he approved it).
IMO