MOSCOW — Fifty years ago, Yuri Fidelgolts was living in forced exile on the Kazakh steppe, the last stop on a decade-long conveyer of punishment, including a frigid Siberian prison camp where a guard reminded inmates daily that a step out of line would mean a bullet in the head.

A few months later, it was over. Nikita Khrushchev had stunned the Soviet Union with his so-called secret speech denouncing the crimes of a man whose merciless rule ruined millions of lives: Josef Stalin.

Free at last, Fidelgolts flew home to Moscow.

"I didn't even take a train, I spent my last money on a plane ticket," recalled Fidelgolts, 78, his words punctuated by coughs evoking the tuberculosis he contracted during his ordeal. "It was a flight of joyous fantasy — like a gift from above."

Khrushchev's speech, sprung on a shocked audience in a closed session on the final day of the ruling Communist Party's 20th Congress on Feb. 25, 1956, dramatically changed the lives of countless Soviet citizens and ushered in a period of relative openness whose motives and meaning remain under debate half a century later.

"He told the people the truth — not the whole truth, but it was the first time in Russian history that a leader has told the people the bitter truth," said veteran human rights activist Lyudmila Alexeyeva, a member of a generation inspired by the secret speech — and the subsequent era known as the Thaw — to push for reform.

Khrushchev opened a crack in the monolithic Soviet system that was pried further open by Mikhail Gorbachev, leading to the collapse of the communist Soviet Union in 1991. But Khrushchev left the system intact and the Thaw was short-lived, giving way to new oppression in the era of stagnation under his successor Leonid Brezhnev.

That brevity — combined with the chilling staying power of Stalin's popularity and the return to tighter state controls under President Vladimir Putin — has prompted some Russians to wonder whether their country is doomed to a cycle of brief bursts of freedom followed by harsh rule.

Still, Khrushchev's revelations, made in what has become known as the secret speech because it was made public only weeks later and published fully in Russia only in 1988, left its audience dumbfounded.

Khrushchev's motives still provoke sharp debate: Some say the speech was a self-interested step in a power struggle, while others call it an act of courage.

Focusing the blame for the state's crimes on Stalin, he stopped short of indicting the Soviet system — leaving a clouded legacy that continues to poison Russia's progress out of a past with which it has never really reckoned.