The nature of the cut which involves dividing the tough left pelvis bone separate from both the right side of that bone, and the spine, would tend to rule out animal activity. The left femur is also still missing in its entirety.
The later bringing of the (left) tibia alone, attached to a wire, back to the search area on the slope in Rock Creek Park, was also unlikely to have been the work of small rodents.
"Any self-respecting squirrel would bet its two front teeth that this was the work of human beings," according to Crystalk, an expert in matters squirrelly.