Norman Jewison, director

Photograph: Andy Hall/The Observer

Not long after I finished In the Heat of the Night, I went skiing in Idaho and my son broke his leg. Sitting opposite me in the hospital was the then junior senator for New York, Robert F Kennedy, whose son had broken his leg too. I told him I’d been working on a film about a black detective in a southern town. He said it could be an important film. He told me timing was everything – in politics, art and life.

It was 1966 and the US was going through traumatic times with the civil rights movement. Cities were being burned down. The Mirisch Company, who were middle men for United Artists, had asked me to adapt John Ball’s book – even though, being from Toronto, I had no connection to the tension on America’s streets.

We reshaped the material, putting the focus on the relationship between Virgil Tibbs, the black detective from Philadelphia played by Sidney Poitier, and Bill Gillespie, the redneck sheriff played by Rod Steiger. Poitier refused to film below the Mason-Dixon line, in southern Pennsylvania, since he and Harry Belafonte had recently been harassed by the Ku Klux Klan in Mississippi.

So we cut a deal. I found a little town called Sparta in Illinois, near the Mississippi river, the most southern location I could find. “If we film there,” I said, “you’ve got to give me a weekend in Tennessee for the scene in the cotton plantation.” When we got to Tennessee, only the Holiday Inn would accept blacks and whites together. The local sheriff said: “Keep your people at the hotel. I don’t want them around town.”

The atmosphere fired up both actors. They ended up improvising a lot of the confession scene at the sheriff’s house, where they bond. We were sitting in the car outside, waiting to shoot, but the rain was so heavy on the roof we couldn’t record. So we just sat and rehearsed – and the scene got more and more intense. I’ll never forget Steiger turning to Poitier and saying: “Don’t get smart, black boy!” I didn’t know if Poitier was going to be offended, maybe ask Steiger not to say that. But we used it. I really lucked out with that rainstorm!

In Tennessee, the local sheriff said: ‘Keep your people in the hotel.’ Photograph: BFI

The famous slap, where Tibbs retaliates against a racist landowner, wasn’t improvised, though, as has been suggested. I kept telling Poitier that Tibbs was a sophisticated detective, not used to being pushed around. I showed him how to do the slap. “Don’t hit him on the ear,” I said. “I want you to really give him a crack on the fatty side of his cheek.” I told him to practise on me. A black man had never slapped a white man back in an American film. We broke that taboo.

Young black people in northern cities responded to the film in a much more visceral way than the whites did. This was the first time a black actor was wearing the fancy suit and being looked up to.

In January 1968, I was given the New York Critics’ Circle award for best drama. And who was presenting but Robert F Kennedy? “I told you the timing was right,” he said. Six months later, he was dead – just after Martin Luther King’s assassination. I left America afterwards. I said to myself: “This is a country where they kill off their heroes. I’ve got to get out of here.”

‘Being looked up to’ … Lee Grant and Sidney Poitier. Photograph: Allstar/United Artists

Walter Mirisch, producer

Photograph: Jason LaVeris/FilmMagic

United Artists were concerned. They feared the film might lead to unrest in the south, even riots. I said: “Suppose it never plays below the Mason-Dixon line? How much do you think we could afford to spend if we just limited the distribution?” They said $2m.

I said to production: “How many shooting days will this buy us?” We came up with a schedule of 40 days. And Poitier signed on for $200,000, well under his usual rate. It was the same year he made To Sir, With Love and Guess Who’s Coming to Dinner. He was the outstanding black actor in film , one of the biggest stars of the whole industry. The fact that he was on board helped tremendously.

We didn’t just get film reviews, we got editorial comment – and all very favourable. Ultimately, of course, the film was released throughout the south and did reasonably well. It’s just as relevant today. I had hoped our country would have made more progress.

Poitier and Steiger, who won an Oscar. Photograph: Sunset Boulevard/Corbis via Getty Images

My father died just before the 1968 Oscars. I was feeling very disturbed and wasn’t sure I’d go. The competition was daunting and I’d no idea if we were going to win. Then King was assassinated and the ceremony was postponed. My family convinced me to go when it was finally rescheduled. My father would have agreed with the movie’s politics, so winning the best film Oscar for such a labour of love was a huge moment for me. It still is.