To answer simply, and bluntly, once you are put on a slave ship, regardless of how - whether via raid, slave merchants, or otherwise, were sold to someone, that individual that was transported to north america would no longer have the legal protections of a human. So, broadly speaking without some specific anomaly like a king or emperor being enslaved and causing broad public outcry, likely with the support of another colonial European power, there is probably an overwhelming likelihood that the first individual would be owed no freedom under US legal process, and even more likely that any African without an immense amount of social and political capital would also be enslaved and stripped of human rights. There was some nuance legally regarding those designated as free men, where more legal protections were offered, and occasionally underground railroad operators and abolitionists would engage in legal battles over individuals status.

The problem was, that the fugitive slave act, both of 1793 and 1850 offered enough agency to slave catchers that they would have the ability to even capture individuals designated as free and force them into slavery. Essentially, because of the racial tensions, the legal oppression and the slave trade industries monetary incentives, slave catchers had no incentive to operate under strict rule, morally, and without the desire to capitalize at any point.

To add more context, here in Canada (except Quebec, where slave trade and chattel slavery existed unfettered until France abolished the practice in its holdings)where slaves were given legal protections and status as 'free men' as slavery was abolished in the , or citizens, slave hunting groups in the US had the ability to cross state lines and recapture a recently freed individual that was considered the property of a slave master. This same mechanism existed in the northern states, where individuals who escaped their masters were located and forcefully brought back to their masters by individuals called slave catchers, who were paid small flat fees for each returned slave. The required evidence to be brought to court heavily favored the slave catchers, as they only had to make a claim to ownership to provide merit to a legal case. The fugitive slave clause was an amendment in the US Constitution (Article IV, Section 2, Clause 3) that also gave broad powers over free black individuals, and fugitive slaves. A decent analogy would be a modern police officers subjective standard of reasonable cause.

Sources: Baker, H. Robert (November 2012). "The Fugitive Slave Clause and the Antebellum Constitution".

Fehrenbacher, Don E. (2002). The Slaveholding Republic: An Account of the United States Government's Relations to Slavery. Oxford University Press

Merriam, John M. (1888). "The Legislative History of the Ordinance of 1787" (PDF). Proceedings of the American Antiquarian Society. Worcester: American Antiquarian Society (published 1889). New Series Vol. V: 303–342.