Heck, entire organizations are devoted to those with “black sheep” kin—the International Black Sheep Society of Genealogists, for one. In addition, there’s a Blacksheep Ancestors blog and a resources site to help you research forebears the rest of the family would rather not discuss.
Trial and error
Up the river
Don’t overlook the possibility your ancestor died while incarcerated. If no one claimed the body, he may have been buried at the prison. Interment.net features a transcription of tombstones from Fort Leavenworth Military Prison Cemetery and listings from a few other jail graveyards. Find A Grave has cemetery transcriptions from institutions such as Stateville Prison in Joliet, Ill.
Old newspapers are invaluable for tracking down criminals in your clan, potentially letting you read about your ancestor’s arrest, trial and conviction. Search the Chronicling America newspaper directory to find titles covering the date and place of your ancestor’s crime; if you’re lucky, that newspaper might be among the searchable collections on GenealogyBank ($69.95 a year) or another subscription site. Public libraries and law libraries may hold accounts of criminal cases involving a notable felon, so check county and legal history books.