Why was Knudsens and Brydesens cars i the neighbourhood on the day of the murder and why does Knudsen snick out of his home to meet a mysterious person?

How is it that Brydesen are locked in his own deep-freeze? Is it nonetheless him who has killed Ellinor Holm, so that two person are in it together?

Why is it so important for the police to ask "Do you like oysters?". Why does the barrister, who is the chairman in Knudsens firm, not like the manager?