One of the most interesting aspects of researching your ancestry is discovering a family member with a criminal record. It can actually be very exciting researching a case like this, as records are often quite detailed. As a genealogist, this is extremely valuable when building a picture of the past, but at the same time it can be disturbing if your ancestor has carried out a particularly heinous crime. Thankfully this has never been the case with me.
There are numerous ways to research historical criminality, including local court records and specialist books. Newspapers should not be ignored as a rich source of information relating to trials. It can also be worthwhile searching online, as some institutions have made their records available. Perhaps the most famous is the Old Bailey online. Another good website, particularly for Scottish ancestors, is for Inverarary Jail. It has historical records of 4345 former prisoners freely available to search and browse.
These are just a couple of examples. I found information of a trial involving my great-grandfather in Grimsby just by performing a basic Google search. In this my ancestor was the victim of the crime rather than the perpetrator.
Researching any criminality in your family history can open up a whole new avenue for you to explore. It should not be forgotten that historically prisoners were often transported to Australia as part of their punishment. If this is the case in your ancestry it will allow you to research passenger lists, and from their your ancestor's new life down under. You may even discover modern day relatives that you never knew you had.
Ultimately, finding a criminal ancestor is interesting because the information discovered gives a good indication of how they lived. Fleshing out the basic data in this way is, I believe, what genealogy is all about.