I think maybe his apartment.
Joran was keenly aware that his father was in the justice system, and that he would be ruined if Joran had a dead girl on his hands. In a way, it was...blackmail. Of course none of them intended to kill her, but the cover up is the biggest sin, IMHO.
Where? On the beach. And he hid the body and came back for it.
You think the coverup was the biggest sin? I dunno, the murder or whatever seems worse to me. Maybe the coverup was a big mistake but whatever went before was bigger.
I think you're right. Joran knew daddy would help him since daddy's life was all about his work. Too bad PvdS was so wrapped up in his career that he didn't realize his son was out of control.
The sins of the son are spotlighting the bigger sins of the father, who, especially as a jurist, should have known better.