While it is not strictly true that she was the only white person who lost her life in that struggle, (Freedom Riders Andrew Goodman and Michael Schwerner were murdered in Mississippi along with James Chaney in 1964), it became clear that Viola Liuzzo was the person in question, having been murdered by the Klan in direct connection with the Selma marches of 1965.
Sometimes being an archival gumshoe means that you uncover stories that tear you up, and my voice broke with emotion as I told my wife about it over supper that night.
I will let the Dictionary of Unitarian and Universalist Biography tell the story:
On March 24 Liuzzo stayed overnight at St. Jude's, a complex of buildings including a Catholic Church, hospital and school, just inside the Montgomery city limits. From the church tower she watched the approach of 25,000 marchers. When she came down from the tower, unsettled and anxious, she told Timothy Deasy, one of the parish priests, "Father, I have a feeling of apprehension. Something is going to happen today. Someone is going to be killed."
Calmer after prayer, she joined the marchers, barefoot, for the last four miles to the capitol building in Montgomery. With everyone else she sang freedom songs and listened to the speeches. When the march was over, Liuzzo met civil rights worker Leroy Moton, who had been using her car all day as an airport shuttle. The two of them drove five passengers back to Selma. When they were dropped off, Viola volunteered to return Moton to Montgomery.
Viola's biographer, Mary Stanton, describes the ride to Selma. "Between the airport and Selma a car full of whites drove up behind them and banged into the bumper of the Oldsmobile several times before passing . . . When they stopped for gas, Moton remembered, white bystanders shouted insults at the integrated group. Further along, the driver of another car turned on his high beams and left them shining into Vi's rearview mirror. 'Two can play at that game,' she said and deliberately slowed up, making the offending car pass her. Finally, when another car pulled up alongside the Oldsmobile while one in front slowed down, Vi had to jam on her brakes. They were boxed in, one of the passengers remembers, but Mrs. Liuzzo seemed to be more annoyed than afraid. As they drove along Highway 80, Vi began singing freedom songs: 'And long before I'll be a slave I'll be buried in my grave and go home to my Lord and be free.'"
Gary Thomas Rowe was a Federal Bureau of Investigation (FBI) informant and a member of the Klux Klan (KKK). According to his court testimony, events transpired as follows. After the passengers were delivered, he and three other members of a KKK "missionary squad"—Collie Leroy Wilkins, Jr., William Orville Eaton, and Eugene Thomas—spotted Liuzzo and Moton stopped at a traffic light in Selma. They followed her car for twenty miles. While she attempted to outrun her pursuers, she sang at the top of her lungs, "We Shall Overcome." About half way between Selma and Montgomery the four men pulled their car up next to hers and shot at her. Liuzzo was killed instantly. Her car rolled into a ditch. Moton escaped injury.