On Friday morning at six o'clock, the door of his cell was opened, and on the bed, stretched at full length, was seen the body of John Montgomery, cold and breathless. The sensation created by this discovery within the jail was most extraordinary; and the assistance of Mr. Box, the surgeon of the prison, having been immediately procured, every effort was made to restore suspended animation, and, when that was found unavailing, to ascertain the cause of death. An investigation was immediately set on foot by the sheriffs; but they failed to discover any circumstance from which it could be inferred that the deceased had been assisted in his design, by any person in or connected with the jail. All search to discover the means of causing death for some time proved ineffectual, but at length, in one corner of the cell, a small phial was found, labelled "Prussic Acid," which at once unravelled the mystery of the unhappy man's death. It was supposed that he had carried about his person, ever since he had commenced the practice of passing forged notes, what he looked upon as an "antidote against disgrace;" but, to say the least of it, he must have been exceedingly ingenious to have concealed the poison so long after his apprehension, as he was frequently searched, supposing that he had employed the same drug to destroy himself, which he possessed before his committal to Newgate. Upon an examination of the letters, to which we have alluded as having been written by him on the night before his death, it was found that in one, which he had addressed to Mr. Box, he gave up his body to be dissected, expressing a wish, however that the heart should be preserved in spirits and conveyed to a female to whom he had long been fondly attached. In that which he wrote to Wakefield, he alluded to their short acquaintance in the jail, and declared that he was perfectly ready to pass into another world; although his letter contained no reference to the means by which the transition should take place. A third letter was found, addressed to the female mentioned in the communication to Mr. Box; but in neither of them was there any allusion to the mode by which he intended to terminate his existence. On the following day a coroner's inquest was held on the body of the deceased man, when a verdict of _felo de se_ was returned; and his remains were interred at ten o'clock at night, in the grave-yard adjoining St. Sepulchre's church.