The word "purification" seems here to be used with reference to its root in the Greek, πυρ, fire

Upon the original publication of "Marie Roget, the foot-notes now appended were considered unnecessary; but the lapse of several years since the tragedy upon which the tale is based, renders it expedient to give them, and also to say a few words in explanation of the general design. A young girl, Mary Cecilia Rogers, was murdered in the vicinity of New York; and, although her death occasioned an intense and long-enduring excitement, the mystery attending it had remained unsolved at the period when the present paper was written and published (November, 1842). Herein, under pretence of relating the fate of a Parisian grisette, the author has followed, in minute detail, the essential, while merely paralleling the inessential facts of the real murder of Mary Rogers. Thus all argument founded upon the fiction is applicable to the truth: and the investigation of the truth was the object.

The "Mystery of Marie Roget" was composed at a distance from the scene of the atrocity, and with no other means of investigation than the newspapersafforded. Thus much escaped the writer of which he could have availed himself had he been upon the spot, and visited the localities. It may not be improper to record, nevertheless, that the confessions of two persons, (one of them the Madame Delue of the narrative) made, at different periods, long subsequent to the publication, confirmed, in full, not only the general conclusion, but absolutely all the chief hypothetical details by which that conclusion was attained.