One of Northrup’s white friends was able to do all the legal and political work necessary, and then travel down to Lousiana to rescue Northrup. And it had to be his white friend instead of his own family, because black people wouldn’t have gotten the same treatment or results, especially in the slave owning states (after Northrup gained his freedom, he wasn’t allowed to testify in the trial against the slave traders who first held him solely because he was black). Even then, it took a bit of luck for the friend to meet up with Bass and find Northrup. Bass himself was so scared of the repercussions that he fled town before Northrup was freed – Bass was literally afraid for his own life for helping a black man. Now, some slaves did manage to escape. Other answers here have given plenty of examples.
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