Since you are suggesting aliens that are soaking in the blood and organs of humans and cattle to absorb their nurtrients because their own digestive systems we made more more efficient by being removed or modified to make them better slaves/drones
...
And it's obvious these aliens want to live in secrecy right?
Figuring its not a common occurance of photographic or video proof they, the aliens themselves, exist ....
So with all this high technology they have, and the abilty to keep this UFO coverup covered up for sooo long....
why would they feel the need to dump the mutilated carcass (evidence) back on the ground?
Why not just vaporize it or some other high-tech alien method of disposing of stuff?