NEW YORK (CNS) -- Revelatory and spellbinding, the exceptional documentary "King in the Wilderness" premieres on HBO Monday, April 2, 8-10 p.m. EDT.

Depictions of violence, a range of mature themes, strong language and racial slurs make the program most appropriate for adults. Yet, given the film's historical content and educational nature, parents may deem it acceptable for mature adolescents as well.

Timed to coincide with the 50th anniversary of the Rev. Martin Luther King Jr.'s assassination -- April 4, 1968 -- the film chronicles a lesser-known chapter of Rev. King's remarkable, if tragically short sojourn: the last three years of his life.

Peter Kunhardt directed "King in the Wilderness" and his sons, George and Teddy, produced it. (Kunhardt Films has been busy lately. "The Newspaperman," their documentary about Ben Bradlee, the legendary executive editor of the Washington Post, debuted on HBO in January.)

By contrast to the approach taken in the Bradlee documentary, which principally relied on the late journalist's own words to recall his colorful life, here Kunhardt employs a chorus of voices of Rev. King's contemporaries to recollect "the most difficult time" in the civil rights leader's career, according to his lawyer and adviser Clarence B. Jones.

With the notable exception of Joseph Califano, former secretary of what was then the Department of Health, Education and Welfare -- who represents the Johnson administration's viewpoint -- the people interviewed, like Jones, were Rev. King's close associates.

Paraphrasing an African proverb, Jones, now 87, says memorably, "If the surviving lions don't tell their stories, the hunters will get all the credit." The depth and breadth of these commentators' experience, together with the historical impact of their collective witness will prompt viewers' admiration and gratitude.

Some participants will be familiar to a wide swath of the audience, like 2011 Presidential Medal of Freedom honoree Rep. John Lewis, D-Georgia -- at 78, the baby of the group -- and unmistakably raspy-voiced singer Harry Belafonte, still charismatic at 91.

Other figures, such as the Rev. C.T. Vivian, another Presidential Medal of Freedom recipient, and Diane Nash, one of the few women in King's inner circle, may be less easily recognizable.

Along with interviews, Kunhardt uses striking candid photographs, behind-the-scenes archival film footage, home movies, TV interviews with King and others and audio recordings of President Lyndon Johnson's phone conversations to create a rich tapestry. Its subject is a period when Rev. King saw his famous dream "turn into a nightmare."

Less than a week after the Aug. 6, 1965, passage of the Voting Rights Act -- arguably the peaceful movement's greatest victory -- the predominantly African-American Watts neighborhood of Los Angles erupted with violent civil disturbances.

Kunhardt employs footage from Rev. King's visit with Watts protesters to underscore how suddenly and rudely things changed for the movement's leadership. They were forced to contend with an outbreak of urban mayhem that threatened to undo their significant gains.

The man who commanded the nation's attention at the Lincoln Memorial in August 1963 struggles to connect with a handful of restless, distracted protestors just two years later. Rev. King still insists people must join hands -- to which someone in the crowd responds, "And burn!"

Profoundly worried about the potential for a race war, Rev. King realized, as he told a TV reporter in 1967, that the movement was in a "new phase of struggle, from decency to genuine equality." Achieving true fairness, Rev. King later tells a Senate committee, will require "the restructuring of the architecture of American society. It's going to cost the nation something."

Following his pivotal speech condemning America's involvement in the Vietnam War at New York's Riverside Baptist Church April 4, 1967, Rev. King confronted his biggest controversy. Although his wife, Coretta, had protested the war, Rev. King had been reluctant to criticize the Johnson administration, which had delivered key civil rights legislation.

Now, however, Rev. King called "my own government the greatest purveyor of violence in the world." Editorial boards of the nation's leading papers, according to the filmmakers, universally condemned the speech, which Lewis called Rev. King's best.

After the Riverside speech, as erstwhile friends abandoned Rev. King, Black Power movement leader Stokely Carmichael questioned the relevance of nonviolent tactics, while FBI Director J. Edgar Hoover hounded Rev. King as an "immoral opportunist." Rev. King felt, in the words of Xernona Clayton, one of his colleagues in the Southern Christian Leadership Conference, that "the nation had turned against him."

"King in The Wilderness" contains numerous arresting images, but none more indelible than that of Rev. King's father, Martin Sr., grieving over his fallen son's casket. Co-pastor with his son of Ebenezer Baptist Church in Atlanta, "Daddy" King was a big man. Yet, as he gazes down, he wails and wails before his massive body collapses into the arms of other mourners.

This tragic scene is indicative of the lasting impact "King in The Wilderness" as a whole is likely to have on viewers.

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Byrd is a guest reviewer for Catholic News Service.