The story of how Pentagon official Daniel Ellsberg leaked thousands of pages of top-secret documents to the media — after coming to the conclusion that the Vietnam War was based on lies — is not a new one.

A couple of films have been made about it in the past and a number of books written, including Ellsberg's own "Secrets: A Memoir of Vietnam".

But this painstakingly detailed and beautifully edited account of what happened before, during and after the disclosure is worth every second of the watching — even if you already know this tale off by heart.

It's not just that the focus is a hugely important chapter in American history and one that everyone who values freedom of speech and expression, never mind holding governments to account, should be interested in.

Sure, that's key to why this documentary matters so much — and why Ellsberg is arguably the most famous whistleblower in the world.

But if that kind of worthy subject matter puts you off, there are plenty of other reasons to go and see the film.

Simply, it's just a great story told in a truly compelling way by filmmakers who have clearly poured their hearts and souls into the project.

The amount of archival footage is astonishing and I loved the way throughout they blended old film and photos seamlessly with present day interviews.

Ellsberg, now a white-haired old man still banging the anti-war drum, gives fascinating testimony about what led him to make such a momentous decision.

He doesn't shy away from his guilt about the part he played in the deaths of so many, as a military analyst at the RAND Corporation, and how it fuelled his actions.

As a Boston Globe reporter points out: "He had an important role in what became the most ridiculously disproportional bombing campaign in the history of the world."

Ellsberg knew it was highly likely that he would go to prison for releasing state secrets to The New York Times and, later, other newspapers, including the Washington Post and LA Times.

But the burden of what he knew — the pattern of lying by successive presidents, the falsified reasons for the attacks, the "unjustified homicide" of so many — was too much for him.

His conscience kept pricking at him and eventually he literally felt he had no choice.

There is a poignant scene in the movie when he meets a draft resister whose speech at a demonstration crystallised his thoughts. He describes how the young man's words felt like an axe splitting his head.

"But what had really happened was that my life had split in two," Ellsberg says, choking back tears. "It was my life after those words that I have lived ever since."

Ellsberg spent months photocopying page after page of a damning report which exposed the lies told to the public about the war.

Once the information was out there, it took on a life of its own. The Nixon administration, in its desperation to discredit him, suffered what one former official admits was a "collapse of integrity of the first order" and ultimately destroyed itself.

The rest — the Watergate scandal, president Richard Nixon's resignation, the end of the Vietnam War with a death toll of 2 million Vietnamese and 58,000 Americans — is, as they say, history.

But while it may have happened almost 40 years ago, Ellsberg's brave example still resonates.

He shone a light on a war predicated on hypocrisy and difficult not to see as senseless. And his actions exposed corruption at the very highest level. This is a fabulous film about a story that can never be told too often.

'The Most Dangerous Man in America' Tradewinds Auditorium of the Bermuda Underwater Exploration Institute tomorrow at 5 p.m.