Chupacabra Brainstorming, Mange, Mutation, or Evolutionary jump?

Let me begin by saying that I do not necessarily believe that the Chupacabra exists.
Moving on.

The Chupacabra legend began in 1995 in Puerto Rico, after a rash of domesticated animal and livestock attacks. Each dead animal was completely uneaten, and had a complete lack of blood. Each also had two puncture wounds somewhere on its body. Eyewitness accounts claim to have seen a bipedal creature with legs like a kangaroo, spines running along its back, and glowing red eyes.

Reports eventually spread to the north american mainland, however, and parts of central and south america. Despite the attacks being identical, however, the reported sightings were much different. Instead of a bipedal blood-sucking kangaroo creature, it was reported as more of a quadruped with hind legs much longer than the front, occasionally with glowing eyes, large fangs and occasionally large claws. Sightings and corpses have been found all over texas and parts of mexico, with most of them looking more or less the same.
The majority of tests done, however, point to these creatures being either Coyotes or domesticated dogs. Skin samples have said that though most of these creatures do not and did not have mange, they at one point had hair on their bodies.

My question is this: What do you think that these creatures are? Obviously there is SOMETHING draining blood from livestock, which even the most hardcore skeptic can admit isn't normal. A creature of that size would have to kill ridiculously large amounts of blood to live solely on that substance. Plus, the attacks have been followed by sightings of these strange creatures, be them Chupies, dogs, coyotes, etc. Are they mutations? An incredibly strange hybrid that learned to breed true? Or are they some odd combination of these facts coupled with a strange evolutionary jump?
Discuss.