Andrzej Wajda has always been a controversial film-maker.
He angered the communist rulers of Poland with trenchant portraits of the wartime Warsaw uprising and the suppression of the Solidarity movement.
But he told me that Katyn was the film he never believed he would make. He knew the communists would stop him, and never thought the communist system would fall in Poland.
But it did, and the film had a premiere in Warsaw on 17 September - the anniversary of the day that Soviet troops entered Poland in 1939.
Katyn is a bleak portrayal of how Soviet troops carried away thousands of Polish officers and intellectuals, imprisoned them in camps and then systematically executed them in 1940.
Mass graves were discovered by German troops in 1943 in Katyn Forest, near the western Russian city of Smolensk. But the Soviet Union always denied responsibility for the massacres. It blamed the Germans and forced the post-war Polish state to do the same.
Wajda's father was one of the executed officers, and he grew up with what he calls the Katyn lie.
"After 1945 the Katyn lie became the basis of the Soviet-Poland friendship," he says.
"Of course, the Soviets wanted us to believe it was the Germans who had committed this crime. However, it slowly came to us that it couldn't have been the Germans, it must have been the Soviets. The lie was given to us in school, everywhere, we were just hearing the lie."
Wajda is now 81, and many believe this will be his last major film.
I asked him what impact he thought it would have on Poland. Would people feel cleansed? Did he think it would change the debate?
"If my film has an impact I hope it's going to be atoning, soothing, because for the first time the crime - the lie - has been shown on the screen," Wajda says.
"The best medicine, the best remedy for political and social problems is to show them and to speak truly about them. So, I hope that it's going to soothe people because we have finally shown the truth."
In her small flat in central Warsaw, Jolanta Klimowicz has an envelope with a handful of faded brown photos of her father, who was also killed in the Katyn massacre.
She was 10 when her father was taken away. The family were never told what had happened to him, and for years her mother hoped that one day he would return from a Soviet prison camp.
But the subject was taboo, so she could not talk to anyone about it.
The Polish communist government blocked all public debate. The families could not even comfort each other.
"All of us, the Katyn children, are obsessed with the tragedy of Katyn and what happened to our fathers. But I remember him, even his smell I remember," Jolanta says.
'Crime and lie'
I asked Wajda if he had found it difficult to make a film on a subject in which he was so emotionally involved.
He answered: "My problem was: what was to be the subject of this film? Was it the officers? That would make it a political movie. Was it my mother, or the women waiting for the officers? That would make it a psychological movie. And that was a very difficult decision to make.
"I realised these two elements had to come together because on the screen we have to see both the officers and the women. And they are being lied to. We have two subjects here: we have the Katyn crime and then the Katyn lie."
Millions of Poles died in World War II.
It was with some difficulty that I found the Katyn cross - one granite memorial among thousands in Warsaw's military cemetery. But here the flowers and ribbons were fresh.
The Soviet Union only released documents acknowledging the massacres in 1990, and the long cover-up means the issue is still current in Polish politics.
A general election is under way in which the government wants to make responsibility for Poland's communist past a central issue.
Wajda worried that his film might become part of the political debate, but so far he has managed to avoid that.
"I am not taking any photos with politicians, I am not giving any political interviews. I am not taking part in the elections - apart from as a citizen, of course. So I am trying to do everything to save my film from being used as a means of political propaganda."
The Polish army runs a small Katyn museum which documents the discovery of the bodies.
Visiting it is a wrenching experience. It has gruesome pictures of the graves and the piles of personal belongings excavated from them - a jumble of spectacles, cigarette cases and boots.
About 40,000 people visit it annually, but I pressed Wajda on whether his film - being seen by millions of people across the country - could not help but change the way people thought about the massacres and relations with Russia.
"I wanted this film to be a farewell, an end to this subject. What I didn't want was for it to cause any political problems, any conflicts. I just wanted it to end the subject.
"Despite the fact it was a crime, I don't believe it should be followed by consequences in the form of any criminal charges for the people involved.
"I think it is very important that this film doesn't become a means of political manipulation."
Finally he added firmly: "I don't owe anything to anybody, this film was not made with public money, so I don't owe anything to any politician."