The license plate of Clas Greve's car is a Dutch diplomatic plate. The letters "CD" (for Corps Diplomatique) on it are issued exclusively for that purpose. But he is not a diplomat and no diplomat may lend him such car.
After Roger Brown has pulled Ove from the lake and they both are in the car, driving to Ove's place, Ove is still dizzy and disoriented and keeps falling on Roger's shoulder. At one point, Roger pushes him away, Ove's pukes a little, and then you see a hand pat Ove on the shoulder. That hand came from back seat, and doesn't belong to either Roger or Ove.