New Human Fossils found

General question here from a non geneticist/biologist/archaeologist/palaeontologist.So they find a skull or a group of skulls that do not conform to our understanding of H. sapiens or other known hominids.
At what point and how do they decide that this represents a new species, and not a single or group of deformed H. sapiens?Is it possible that this "new" species could be the remains of some kind of deformed or mutated already-known type?Genuinely interested to know how they decide this given the scarcity of these specimens.

Hmm.. ok.. that doesn't really enlighten me much..So.. From this Story:
New human species identified from Kenya fossils - BBC News"Anthropologists have discovered three human fossils that are between 1.78 and 1.95 million years old. The specimens are of a face and two jawbones with teeth. "how does the use of Multivariate statistics indicate that this is a new species and not just 3 individuals with physical deformities?

That doesn't seem to explain how three pieces of bone could be confirmed as an entirely separate species and not just an aberration in a single, or handful of individuals.

I guess I don't see how that method can apply to a sample of 3 bones.Genuinely trying to find out how this was deemed to be a new species.