It is not a cat! That is a "fisher cat" - which is actually a member of the weasel family, and it is a predator by nature. They are usually just called fishers, but some people do call them fisher cats even though they are not at all feline. That must be a young fisher as well, as it is pretty small. They are voracious hunters, and have been known to kill pets left out unsupervised when the opportunity arises.