Hard to resist such an invitation.
Commander Patten was unequivocal in his statement that Stephenson had refused to speak to police, on any matter. He repeated this a few times in updates, that nothing had changed in that regard, no speaking, at all. While I am not discounting the idea of perhaps a confession in sign language, Patten , I am sure , would have categorised that as communication. But he was adamant. No communication came from Stephenson.. .
As to the waiting to pick him up, it is possible that VICPOL hoped he would return to where he had the body. This is not a useless hope, many killers do exactly that, shift it around, remove it to a new site, etc, it seems a rational thing to do, do you think? Also, perhaps they watched him to see who his peers were and what part they played, if any, in this crime, and since no one else has been arrested, maybe it's fair to say no one else was...... But at some point, a decision was made to pick him up, maybe he rang a travel agent, or booked a place far away, something like that, that provoked a sudden move by VICPOL to bring him in . ....