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“The hanging.”

For years, Karen Branan, a white woman from Georgia, kept at a safe distance the haunting words that her grandmother had spoken. Ms. Branan was an inquisitive journalist, but she refused to explore a hanging that her grandmother had said was one of her most unforgettable memories. She was afraid of what she might learn.

But in 1986, when she learned that she was going to have a racially mixed grandchild, Ms. Branan felt compelled to dig up the truth. She discovered that her relatives had been part of a mob that had lynched four black people — three men and a woman — in Hamilton, Ga., in 1912.

Ms. Branan turned what she learned into a book, “The Family Tree,” that was published two years ago.

The book eventually made its way into the hands of Jackie Jordan Irvine, an Alabama native and a professor emeritus of urban education at Emory University. Ms. Irvine, who is black, came across the name of her ancestor Milford Moore. He was related to John Moore, one of the lynching victims.