One of the students who...

Which is the correct verb after the relative pronoun who in the sentence below?

(1) One of the students who (was, were) here is John.

Is it was or were?

The answer depends on whether the relative pronoun who refers to students or the head noun One. Accordingly, we can rewrite (1) to illustrate this difference in interpretation:

(2) Of the students, one who was here is John.

(3) Of the students who were here, one is John.

Sentence (2) corresponds to the interpretation in which who refers to the head noune One, and so was is the appropriate verb. Sentence (3) shows that who refers to the plural students, and so were is the appropriate verb.