TV review: Martin Luther King and the March on Washington, BBC2

It has become a story about speeches – or bits of speeches. The latest came yesterday with President Obama's address before the Lincoln Memorial, 50 years to the day after a black man had a dream on the same marble steps. His words have played on loop for half a century, but what do we know about the story behind the soundbite, about the content of his character and of those who marched for a new America?

Martin Luther King and the March on Washington expertly replaced a speech, the climax of which was improvised, in the context of a momentous summer. Eight years after Rosa Parks had refused to give up her seat on that bus, the fight for civil rights was losing momentum. Its leaders, including King, realised the need for something big. Given fresh impetus by the brutal police response to protests against segregation in Birmingham, Alabama, they set about taking their struggle to the heart of the union.

Organisers had just six weeks to plan the March for Jobs and Freedom. Among the most gripping sequences in a supremely authoritative documentary were those that focused on logistics. Planes were chartered from LA, some carrying Hollywood's leading lights. Thirteen special trains and a fleet of 972 buses came from New York City alone. Many more rolled through the night from the Deep South towards the capital at a rate of 100 per hour.

Despite the fears of a paranoid FBI, and concern in the White House that a sympathetic John F Kennedy might become the president who sponsored a riot, there was a sense this was an irresistible movement. King was its face and his people's time had come. Behind the scenes, however, there was hesitation. John Lewis, a young activist, delivered the second-most important speech of the day, but not before debate about its revolutionary tone. Following King's advice, he agreed to soften it.

By the time the man himself took to the podium, more than 200,000 people had gathered. Millions more watched on TV. King's notes excluded the "dream" that he had talked about in earlier speeches. As his latest address approached a close that fewer people would remember, Mahalia Jackson, the gospel singer, shouted up the steps to her friend: "Tell them about the dream, Martin, tell them about the dream!" So he did, improvising the line now carved into the step on which he stood. It has lost none of its power to raise goose bumps.

Sidney Poitier, Harry Belafonte, Diahann Carroll and Joan Baez were on the march and were among the talking heads. Denzel Washington narrated. Oprah featured, too, having watched King speak as a nine-year-old. "Everything that has happened to me," she said, "my ability to be liberated, to be completely free, to determine my own destiny... happened because of that moment."

Kennedy was assassinated just three months after King's speech. But, the following year, the civil-rights bill that he had proposed became law. Four years after that, Dr King would go the same way, killed by a sniper's bullet. To tell that story, the equally riveting MLK: the Assassination Tapes used archive footage, photographs and newsprint as it pieced together the story of King's murder and legacy.

What had started with a strike by black bin men in Memphis descended into violence. King appealed for calm on both sides. On 4 April, 1968, he was shot in the face – and the world reeled. His dream barely realised, he had alluded to death threats the day before in a less famous speech. "I would like to live a long life," he said. "But I'm not concerned about that now… I've seen the promised land. I may not get there with you. But I want you to know tonight, that we, as a people, will get to the promised land."

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