When Van der Valk and Lucienne are talking to Gert and Marian at the vigil, Gert and Marian are facing them over the railing. When the camera switches to Eddie and Citra's viewpoint, on the other side of them, Gert and Marian have their backs to the railing and are looking over their shoulders at Van der Valk and Lucienne.
The murders are committed with a Colt 1911 pistol. It is identified as having been sold by an Amsterdam gun club, but there is no mention of who bought it. The impression is given that gun clubs in the Netherlands can sell guns without keeping any record of the purchaser. This is not the case at all, and Dutch gun control laws are in fact strict.
When driving to the scene of the shooting neither Piet, Lucienne nor the rear seat passenger were wearing seat belts. The wearing of seat belts is compulsory in the Netherlands.