Redundancy:
We want to film the courier picking up the credstick and leaving the pixie. Once he has done that, we apprehend him, verify that there is money on the stick and get the confession from him that he was just selling a pixie for the farm.
The Vamps (hopefully) don't come into play - not that it would be bad to shoot some, but it increases the risk that the courier is injured or killed before he can confess - or worse escapes.
Since we know the drop point it's probably easier to wait there for the courier since it's easier to hide stationary then to follow with three people after one person inside sewer tunnels.