As well as Bodleian History location, SOLO searches may reveal that the Vere Harmsworth Library (University of Oxford's principal research library for US studies) has useful material too. Examples in box to right.
There is a specific subject heading for this instance Trials (Witchcraft) -- Massachusetts -- Salem -- History -- 17th century
You may find that the Bodleian Vere Harmsworth Library has the only Oxford copy for this topic!