My dog injuried a baby possum, what should I do with it?

My dog left a possum on my back porch, its looks messed up and all chewed onbut breathing, it perhaps has puncture on its back. It does move its legs and tail. Its quite morbid. I feel bad for just leaving it there to possibly die a painful death, should perhaps kill it? its 11pm here now, I doubt animal control is around and if so they probably wont give a hoot. What to do??