The fugitive slave law of 1850 put the burden of proof on captured blacks, but gave them no power to prove their freedom. Any claimant could bring an alleged fugitive before a federal commissioner ( a new office created just for this)...to prove ownership by an affidavit from a slave state court or of white witnesses. If the commission decided against the claimant he would receive a fee of 10 dollars, if they decided for him he still received a fee of ten dollars. The law also required U.S. Marshals and deputies to help slave owners capture their property and fined then$1000 if they refused( a pretty penny back then) It empowered marshals to deputize citizens on the spot to aid in seizing a fugitive and imposed stiff penalties on anyone who harbored a fugitive or obstructed his capture. The expenses of capturing and returning a slave were borne by the federal treasury not the state.

A fugitive who has no protection of habeas corpus, no right to trial by jury form to testify in his behalf, does not ( to me) seem like a safe guard of personal liberty.