fugitive slaves and offering sizable rewards for their capture and return. Federal marshals and professional bounty hunters known as slave catchers pursued freedom seekers as far as the Canada–U.S. border. "Reverse Underground Railroad" Freedom seekers were not the only black people at risk from slave catchers. With demand for slaves high in the Deep South as cotton was planted, strong, healthy blacks in their prime working and reproductive years were seen and treated as highly valuable commodities. Both former slaves and free blacks were sometimes kidnapped and sold into slavery, as in the well-documented case of Solomon Northup, a New York-born free black who was kidnapped by Southern slavers while visiting Washington DC. "Certificates of Freedom," signed, notarized statements attesting to the free status of individual Blacks also known as free papers, could easily be destroyed or stolen, so they provided little protection. Some buildings, such as the Crenshaw House in far-southeastern Illinois, are known sites where free blacks were sold into slavery, known as the "Reverse Underground Railroad". Fugitive Slave Act of 1850 Under the terms of the Fugitive Slave Act of 1850, when suspected fugitives were seized and brought to a special magistrate known as a commissioner, they had no right to a jury trial and could not testify on their own behalf. Technically, they were not accused of a crime. The marshal or private slave-catcher needed only to swear an oath to acquire a writ of replevin for the return of property. Congress was dominated by Southern congressmen because the population of their states was bolstered by the inclusion of three-fifths of the number of slaves in population totals. They passed the Fugitive Slave Law of 1850 because of frustration at having fugitives from slavery helped by the public and even official institutions outside the South. In some parts of the North, slave-catchers needed police protection. Arrival in Canada British North America (present-day Canada) was a desirable destination, as its long border gave many points of access, it was farther from slave catchers, and beyond the reach of the United States' Fugitive Slave Acts. Further, slavery ended decades earlier in Canada than in the United States. Britain banned the institution of slavery in present-day Canada (and in most British colonies) in 1833, though the practice of slavery in Canada had effectively ended already early in the 19th century through case law, due to court decisions resulting from