Roughead's The Trial of Deacon Brodie describes the robbery of John Tapp's house as:

Brown appears entitled to the credit of planning the next robbery, and took a leading part in its execution. In those days the merchants of Edinburgh usually resided above their business premises, and the key of the shop was hung on the inside of the door—a habit highly appreciated by the Deacon's little band. Brown brought to Smith the key of a shop belonging to one John Tapp, which, he said, also opened the door of that gentleman's house; and Smith, having cast a professional eye over same, assured him " there was nothing in it." Thereafter, one evening about Christmas time,between nine and ten o'clock, Brown dropped in upon John Tapp, whom he detained in his shop over a friendly and seasonable bottle. His associates, meanwhile, opened the house door with a false key and rifled the good man's repositories, making off with "eighteen guinea notes, and a twenty shilling one, a silver watch, some rings, and a miniature picture of a gentleman belonging to Tapp's wife, which picture they broke for the sake of the gold with which it was backed.” One wonders if Mrs. Tapp mentioned the loss to her husband. These valuables accompanied the mace to Chesterfield, where

John Tasker alias Murray seems to have driven a brisk, though illegitimate, trade, along with a letter to him, written by Brown in Smith's name, arranging for their disposal.

On George Smith's 10 March 1788 statement to Sheriff Archibald Cockburn, this is recorded about the Tapp robbery:

[George Smith] Declares that, since the mace was stolen, as the declarant thinks, the declarant, along with Brown and Ainslie, laid a plan of breaking into John Tapp's house and taking his money; that this business was suggested, and pressed, by Brown, the declarant rather being averse to it; that Brown told the declarant that he knew the key of Tapp's shop opened the door of his house, and brought it to the declarant to look at, which, upon seeing, the declarant said there was nothing in it, meaning ny that, that the lock to which it belonged could easily be opened.

Declares that, accordingly, soon after this, and, as he thinks, about Christmas or near to it. Brown kept Tapp in his shop drinking, and the declarant and Ainslie, betwixt nine and ten o'clock at night, opened the door of the house with a false key and took out of his drawers eighteen guinea notes and a twenty-shilling one, a silver watch, some rings, and a miniature picture of a gentleman belonging to Tapp's wife, which picture they broke for the sake of the gold with which it was backed.