There was a question submitted about this a few years ago: https://www.reddit.com/r/AskHistorians/comments/199hrj/did_the_federal_government_of_the_united_states/

There were a whole host of slavery-related questions about 2 years ago when Django Unchained came out.

This answer is probably the closest to a real answer to your question: https://www.reddit.com/r/AskHistorians/comments/19991h/another_django_unchainedinspired_question_what/c8lzb4d

In summary, the state and local governments sometimes "owned" slaves as part of the probate process. Slaves were legally considered a form of personal property and treated as such by the probate courts. In the event a man died without heirs, his property (including slaves) would escheat to the state, which would generally auction off the property as soon as possible.