Scavengers of all species frequent rivers and other water sources, swamps, ponds, etc.. The closer the remains are placed to a water source, the faster the elimination of incriminating and indictable evidence.
The sandy soil found near the banks of a river would provide for easier digging (should a shallow grave be used). Due to the sunlight provided by the clearing space, the weeds and underbrush would flourish, concealing the bodies or shallow graves, as shown in the photo. The tree roots, accumulation of leaves, and thick canopy in the adjacent forest would discourage underbrush growth and allow a less than desirable concealment of the bodies or shallow graves. jmho