Who was he?
"In the first place, we find him committing a secret crime from which John Blackmore alone will benefit.

This suggests the prima-facie probability that he was John Blackmore.
"Then we find that he was a man of normal eyesight who was wearing spectacles for the purpose of disguise.

But the tenant of New Inn, whom we have seen to be, almost certainly, John Blackmore--and whom we will, for the present, assume to have been John Blackmore--was a man with normal eyesight who wore spectacles for disguise.
"John Blackmore did not reside at New Inn, but at some place within easy reach of it.

But Weiss resided at a place within easy reach of New Inn.
"John Blackmore must have had possession and control of the person of Jeffrey.

But Weiss had possession and control of the person of Jeffrey.
"Weiss wore spectacles of a certain peculiar and probably unique character.