I don't imagine such a database on records of criminality will be too easy to get hold of. I don't know about in the US, but in the UK you have to request such information through legal channels.
Such entities which can do this are organisations, for instance when you complete a CRB check. CRB checks are often paid for by the employer, and seldom by the employee, depending on the organisation's policy.
By the looks of those sites, such information is more freely available in the US, but I still wouldn't expect them to be downloadable by anybody in a nice SQL format. You would no doubt have to submit an application to the FBI agency because of privacy issues and the data protection act (if that is applicable in the US. I am confident it will be in one form or another).
The man who comes back through the Door in the Wall will never be quite the same as the man who went out.