In 1796, when slavery remained both legal and common in New York, a white man named Aquila Giles set out to free Hannah, a 30-year-old woman he enslaved, and her daughter, Abigail, who was about 5.

The revelation came during a cross-examination in Paul Caneiro's trial for the murders of his brother's family. The Union County mayor and police force are accused of discriminating against minorities ...