In North Carolina records I have seen first person accounts by slaves during the coroner's inquest stage of a murder investigation. I do not know if South Carolina has such a record series as coroner's inquests.
In North Carolina I have also seen a couple of slave courts dealing with murder committed by a slave that included testimony of a slave. If memory serves that record is in Northampton County records just prior to or at the outset of the Civil War (early 1861, is my recollection).
Sorry, my knowledge is limited to NC records.