Smith forged manuscripts from various historical people, such as Mary, Queen of Scots; Oliver Cromwell; and Sir Walter Scott.
Letters were dated wrongly, sometimes after the death of their supposed writer, and had been written on modern paper with new writing implements.
One reader of the paper found out that the person the letter had been addressed to, weaver John Hill, had never existed and begun to suspect the authenticity of the whole collection.
Colvill Scott of Surrey, historical document expert, also announced that there were dozens of letter forgeries all over Scotland.
Another reader noticed that one of them, The Poor Man's Prayer, had been published when Burns had been only a child and was the work of William Hayward Roberts, who had also written the other poem.
An American collector, who had bought 2020 letters from a manuscript seller, James Stillie, in Edinburgh, heard the rumors about forgeries and sent them to the British Museum to be verified.
When police questioned Smith, he said that he had been employed as a chief clerk of the lawyer Thomas Henry Ferrie, who had asked him to get rid of old documents in the cellars of his law office.
One of the witnesses was a bookseller Bristo Brown, who had bought large number of Smith's letters and said that he had believed them to be genuine.