American folk singer and activist Pete Seeger (left) adopted and helped popularize "We Shall Overcome" by teaching the song at rallies and protests. Here he sings with activists in Greenwood, Miss., in 1963. Adger Cowans/Getty Images hide caption

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A white heckler arrested during an anti-segregation demonstration in Lexington, Ky., is hustled into a police car in August 1963. Forty years later, the Lexington Herald-Leader ran a correction apologizing for the newspaper's lack of coverage of the civil rights movement. AP hide caption

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More than 200,000 gather on the Washington Monument grounds before marching to the Lincoln Memorial on Aug. 28, 1963. AP hide caption

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A spectator on the National Mall holds an image of President Obama and Martin Luther King during the 2013 presidential inauguration in January. Gabriel B. Tait/MCT/Landov hide caption

itoggle caption Gabriel B. Tait/MCT/Landov

Clarence B. Jones, legal adviser to Martin Luther King Jr., takes notes behind King at a press conference regarding in Birmingham, Ala., in February 1963. Ernst Haas/Getty Images hide caption

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Rep. John Lewis, D-Ga., speaks Saturday at the Lincoln Memorial during activities to commemorate the 50th anniversary of the March on Washington. Michael Reynolds/EPA /Landov hide caption

itoggle caption Michael Reynolds/EPA /Landov

Clarence B. Jones this month in Palo Alto, Calif. As Martin Luther King Jr.'s attorney and adviser, Jones contributed to many of King's speeches, including his famous speech at the March on Washington in 1963. Norbert von der Groeben/Reuters/Landov hide caption

itoggle caption Norbert von der Groeben/Reuters/Landov

George Whitmore Jr., a 19-year-old unemployed laborer, is shown in a Brooklyn, N.Y., police station on April 25, 1964, after his arrest in the Career Girl Murders. Jack Kanthal/AP hide caption

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Joseph Burden (third row, third from right) with his graduating class at Washington, D.C.'s Metropolitan Police Department training academy in 1960. Every officer on the force was required to work the day of the March on Washington. Courtesy of Joseph Burden hide caption

itoggle caption Courtesy of Joseph Burden