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As far back as he can remember, George McCann lived in fear. When he was asleep he would have horrific nightmares filled with violent images. When he was awake, he often felt threatened by people, including members of his own family. And when he felt threatened, he would become aggressive, even violent.

George spent his childhood certain that something very bad was going to happen. And when he was 12, it did. His unrelenting fears led to a violent outburst at school. And George landed in a psychiatric hospital.

It all started on a former plantation in Tennessee. That's where Sandra Arnold's great-grandfather, Ben Harmon, who was born a slave, is buried next to his wife, Ethel. Their final resting spots are clearly marked, gravestone and all, but next to them, Arnold noticed an entire area of unmarked slave graves. She wondered if they could be family, too.

Her research started on that plot, then expanded to the state of Tennessee. Eventually, Arnold learned that it wasn't uncommon to find unmarked slave burial places across the country.