@Kamaji He did this while living in Virginia. Both he and the man he enslaved came here as indentured servants,not slaves. IIRC,Johnson argued in court that it would be impossible for HIS indentured servant to ever work off the bill he was accruing daily,and those were the grounds for enslavement.
When Johnson died,he was a wealthy man living in Maryland raising and selling race horses.
I never did learn what happened with the man he had enslaved,but assume he went to Maryland with Johnson,and died as a slave.