JOHNSTON, J. The murder of a slave, appears to me, a crime of the most atrocious and barbarous nature; much more so than killing a person who is free, and on an equal footing. It is an evidence of a most depraved and cruel disposition, to murder one, so much in your power, that he is incapable of making resistance, even in his own defence . . . and had there been nothing in our acts of Assembly, I should not hesitate on this occasion to have pronounced sentence of death on the prisoner.ML/NJ. . . From the context, and taking every part of the section [of the act of 1791] under consideration, there remains no doubt in my mind respecting the intention of the Legislature; but the judges in this country . . . have laid down, and invariably adhered to, very strict rules in the construction of penal statutes in favor of life . . .
. . . judgment in this case should be arrested.
From my reading, Johnson is saying that killing a slave is very bad, and if it had been up to him, Boon would have been convicted. But the way the law had been written by the Assembly meant that his lower court conviction had to be overturned ("the judgement arrested").
That judges might have been purchased in this case doesn't seem to have occurred to you.
So you're suggesting that slave murder was technically illegal, but that slaveowner money and power corrupted the legal system and insured that the crime wasn't punished. A distinction without difference, it seems to me.