Talented and prolific documentary filmmaker Alex Gibney has spent years looking at the ethically tainted side of human affairs. After examining mindboggling financial corruption in “Enron: The Smartest Guys in the Room,” charting the sex scandal of New York Gov. Eliot Spitzer in “Client 9” and exploring torture practices of the U.S. military in the Oscar-winning “Taxi to the Dark Side,” Gibney was ready for a change.

A couple of years ago he decided to do an uplifting sports story. Thing is, the subject he chose was Lance Armstrong. The champion cyclist had an irresistible story line. Survivor of testicular and abdominal cancer and brain surgery. Seven-time Tour de France winner. A dash of controversy surrounding allegations of drug use and the many medical tests apparently exonerating him. Having retired in 2005, he was mounting a 2009 comeback at the old age of 38.

Before the film was finished, doping authorities finally had the goods on Armstrong. A 164-page report laid out, in detail and with the testimony of his U.S. Postal Service cycling teammates, how he made doping a virtual condition of service on the team. Facing a potentially ruinous lawsuit from sponsors, Armstrong made a public confession to Oprah Winfrey, the first stop on any public redemption circuit. In January, under her sharp questioning, shown here, he confessed that he won his titles shot full of growth hormone, cortisone, EPO, steroids and testosterone. If Gibney had set out to make a cheerleading biography of Michael Vick or Tiger Woods, it could not have gone worse.

But from the ashes of his intended project, Gibney has fashioned something valuable. Reconfiguring his footage and adding himself to the mix as narrator, he has created an unforgettable portrait of an egotist unshakably convinced of his own greatness. Armstrong, an outspoken atheist, repeatedly frames his long-shot cancer recovery as “a miracle.” Ever burnishing the Lance legend, he always treated his critics like annoying gnats, or worse. In the film, former teammates describe him as an intimidating bully.

“The Armstrong Lie” lays out the details of the disgrace in Gibney’s usual painstaking detail, but doesn’t add much to the public record. In place of revelations, it offers us the chance to see Armstrong close up post-Oprah, still without contrition, still single-mindedly spinning the narrative to his advantage. Gibney’s offscreen voice asks pointed questions with investigative zeal. Armstrong evades or mouths unfelt apologies and extenuating circumstances, his eyes as dead as a great white shark’s. Yes, he doped, but so did everyone else struggling up the Alps (Gibney’s film makes a persuasive case that the storied race truly is a rolling drugstore) so what unfair advantage did he exploit? Winners do what it takes to win. And it is all about winning.

He rationalizes that admitting to years of systematic doping and deceit would have hurt too many people. His charisma brought attention to the bike-racing circuit. The myth that the public loved so fervently earned him tens of millions through endorsements. He wrote two self-glorifying autobiographies and the public credulously made them bestsellers. His Livestrong cancer foundation raised hundreds of millions. He gave the sick hope. The good/bad balance sheet in Armstrong’s head made him feel entitled to engage in immoral behavior.

The tale has plenty of resonance off the race course. As sportswriter Dan Coyle says in the film, “It’s not a story about doping, it’s a story about power.” It demonstrates how money debases sports, how the media turn a blind eye to a big lie in plain sight, how institutional safeguards are corrupted, how sponsors choose profitable falsehoods over unpalatable truths.

It also explains why Armstrong was so fast on the bike.

He is hollow.