Use Discovery to search the National Archives (UK) collections for these reports which include original letters and reports from judges on cases and criminals plus petitions for commutation of sentence or free pardon. To search for these, and other convict records, enter a surname, place or crime committed and refine the results by HO - Home Office. Returns can include the Judges' Reports on Criminals (1783-1830). If the record has been digitsed that you can download it from the site (a small fee applies). Otherwise you can request a quotation for a copy to be digitised or printed and sent to you.
Note: The former DocumentsOnline service has now been replaced by Discovery.