In addition, the high demand for slaves in the Deep South and hunt for fugitives caused free blacks to be at risk of being kidnapped and sold into slavery, even if they had their "free" papers. There were numerous instances of people who were legally free and had never been slaves being captured and brought south to be sold into slavery. The historian Carol Wilson documented 300 such cases in "Freedom at Risk" (1994) and estimated there were likely thousands of others.