Geoffrey Mason had begun the day expecting to oversee TV coverage of sports such as boxing, swimming and volleyball. Hours later, he found himself staring at German machine guns and being ordered to turn the cameras off.

The story of how Mason’s control room responded to the hostage siege at the 1972 Olympic games in Munich is told in September 5, a thriller starring John Magaro and Peter Sarsgaard and directed by Tim Fehlbaum. The film follows the ABC Sports team as they turn their cameras on the news – the first time a terrorist attack would be broadcast live to a global audience.

“We had been trained how to tell stories with integrity,” Mason, 83, says via Zoom from his home in Naples, Florida. “That was never in doubt that day. Were we a little nervous about taking some risks? Yeah, but you’re in the heat of the battle, so to speak, and you do what you think is right and, fortunately for us that day, we had the training to to come out ahead of it.”

Mason was born in Englewood, New Jersey, and served in the US navy as a planning officer for an admiral in San Diego, California. He taught the admiral how to sail and, when an opportunity arose for Mason to work locally as a runner on an ABC sports show, the admiral helped him get the job. It was the start of a sports broadcasting career that would span more than half a century.

Mason worked as a production assistant at the 1968 Winter Olympics in Grenoble, France, and Summer Games in Mexico City, Mexico, so he and the TV executive Roone Arledge knew each other well. They also knew that Munich would be different, coming just 27 years after the end of the second world war.

September 5 begins with period footage that says of the Olympic opening ceremony: “It was a starting signal for a peaceful post-war Germany to share itself with the world and an Olympics full of sporting sensations.” Planning an interview with the US swimmer Mark Spitz, Marvin Bader (played by Ben Chaplin) asks: “So you want to ask a Jew about the Holocaust on live television?” Arledge (Sarsgaard) replies: “Yeah. Ask him what it’s like to win a gold in Hitler’s backyard.”

West Germany was eager to erase the stain of the 1936 Games in Berlin that Hitler had sought to turn into a showcase for Aryan supremacy. Munich introduced the first Olympic mascot, the dachshund “Waldi”, and its official motto, “the cheerful games”, tried to project a feel-good spirit.

Mason, who at times speaks with a cool detachment reminiscent of astronaut Neil Armstrong landing on the moon, reflects: “We were aware that the people of Munich and Germany wanted to erase whatever awful memories were left over from from Berlin in ‘36.

“They worked hard and we got to know them in preparation for the ‘72 games. We got to know them as human beings and as people who wanted to put on a good show, as did we. It was almost like we were helping each other present a fantastic experience for the athletes. That was what we were all after and then, of course, it went horribly wrong for them and for the world, actually. Life is about succeeding and failing and you have to learn how to respond to both extremes.”

The peace and goodwill were shattered in the early hours of 5 September. Eight Palestinians from the “Black September” group raided the Olympic village. They infiltrated the Israeli living quarters and killed an Israeli weightlifter and wrestling coach before taking nine others hostage.

Mason, on the early shift on what expected to be a slow day, drove from the Sheraton hotel to the broadcast centre. “When I got there, I realised something was horribly wrong,” he recalls. “There were a lot of people, a lot of police cars. At 5.30, six o’clock in the morning one would not expect a lot of traffic in that area, even though our broadcast centre was literally a hundred yards from the Olympic village.

“Our total focus was to work closely with our allies in the engineering and technical department to prepare ways that we could tell this story that was right next door to us, so to speak.”

Suddenly Mason was thrust into a position of responsibility. He and his colleagues wheeled a big, heavy camera out of the studio for about 100-120 yards, and up about 20ft, to a dirt berm overlooking building 31, where the drama was unfolding. They also had a camera on the Olympic tower that could be trained on the building’s roof. ABC’s Peter Jennings and other reporters were across the alley from building 31 describing by phone what they were seeing.

It was the biggest test of their careers but they felt ready. “As soon as we realised that people’s lives were at stake 100 yards away, yes, it became probably more important than anything we had done. But getting it done wasn’t totally overwhelming. We had confidence in ourselves. We had confidence in our systems and working for someone like Arledge that’s what you learn. You just learn how to react.”

The film recreates the control room with impressive attention to period detail, including authentically clunky 1970s cameras, landline phones, TV monitors and playback machines. It also raises ethical questions but is nimble and wise enough to avoid moralising. At one point the Mason character asks: “Can we show someone being shot on live television?”

Mason explains over Zoom: “That was one of the first things we discussed: what are we going to do if we happen to be in a position of potentially watching someone be killed live on TV? What we decided was, since we didn’t have any good live camera positions, any coverage we had would likely be on film or tape so that we’d be able to judge at some point subsequent to whatever happened, whether or not it was appropriate for feeding out on television.”

Such questions have haunted editors ever since. The September 11 terrorist attacks on New York and Washington played out on live television; footage of planes flying into the twin towers has been replayed countless times. Last week the murder of UnitedHealthcare chief executive Brian Thompson in New York was captured on camera, presenting another dilemma in how much to show viewers.

Mason comments: “It’s tough. Arledge always told us: ‘Just go with your instincts. We knew a lot about you, Mason, when we hired you. We learned to trust you once we all started working together and so there’s nobody on this team with us here in Munich whom I wouldn’t trust in terms of instincts and reactions.’

“That’s what working together prepares us for, to trust each other, to trust ourselves and to do as best we can. After all, that’s all we can do. We can only do the best we can and it was quite a challenge that day but I think, on balance, we did a good job.”

The Palestinian attackers demanded the release of prisoners held by Israel and two leftwing extremists in West German jails. They castrated one of the Israeli athletes before he was shot dead and tossed the body of the other out on the street. West German authorities engaged in negotiations but lacked experience in dealing with such crises.

Thanks to the ABC cameras, the standoff was being watched by millions of people around the world. But what Mason and his team had not considered was that it might include the perpetrators themselves. “That was perhaps the most stressful moment of the day for me,” he admits.

“We were on the air live and the door to the control room, which was right in front of where I was sitting, burst open, and in came several German police with machine guns aimed right at me because I was the first person they could see. They started waving their hands: ‘Kamera aus! Kamera aus!’ I said: ‘English please. What are you talking about?’

“I began to understand what I thought they were mentioning but I wanted to delay it by seconds if I could. ‘Kamera aus. Please, camera off.’ They pointed to the monitor, which showed the output of the camera on the Olympic tower, looking down at the roof of building 31, which at that moment was showing German police sharpshooters crawling across the roof, getting ready to stage what we were assuming was a raid on that apartment in order to rescue the hostages.

“What none of us had thought about until this moment was oh my God, if they are in that apartment, those hostages and their captors, if they are indeed watching the Olympic broadcast cable system and if they indeed are tuned on let’s say it was channel 37, which on the list would have said ‘ABC beauty shot Olympic Tower’, they would be seeing everything that we were seeing.”

Mason duly turned the camera off for some hours but turned it back on later in the afternoon. This was not the only battle for the ABC sports team. The ABC news department wanted to seize control of the story even though they were thousands of miles away. But Arledge insisted that sports would be keeping the story.

Mason recalls: “We all felt very strongly that we’re a hundred yards away. Why do we want someone from a new studio in New York, be they good or bad – who cares? Why would we think that they’re better equipped to handle this story than we are being a hundred yards away?

“We were aware of that disconnect between news and sports but it had never slammed us in the face like it was slamming us in the face at this moment. Thank God Arledge gave us all the leadership we needed at that moment: it’s ours, we’re keeping it, we’ll discuss why or where later but for now we’re going to do it.”

Eventually the kidnappers were transferred to an airfield, along with their hostages, under the guise of meeting their demands. But amid a botched German rescue attempt, the Palestinian kidnappers opened fire on their hostages and hurled a grenade inside one of the helicopters in which the Israelis were bound.

Mason and his team had to report the worst possible news: a total of 11 Israelis had been killed. He remembers the impact it had on Arledge, who typically sat in the front row of the control room and never turned around.

“I never saw his face; I always saw the back of Roone’s head. But in this particular instant, I said: ‘Roone, they’re all dead.’ He said: ‘Can I go with it?’ I said: ‘You can go with it.’ He turned around and looked at me and I will never forget the look on his face. I said: ‘Go with it.’”

Arledge then gave the go-ahead to ABC sportscaster Jim McKay to announce to the world: “They’re all gone.”

Only later did Mason have time to dwell on the unfairness of it all. “Here we were watching these kids do the best they’d ever done and being trained to do what they did best and it was just so unfair that they never had that opportunity.”

He and his colleague Don Ohlmeyer went back to the Sheraton hotel “having had no time to decompress, elevator up, 12th floor or whatever, we had connecting rooms, built ourselves a nice, tall vodka cocktail, sat down and cried like babies. That was the first time that I had allowed myself to feel anything. Whenever I revisit this day, this experience, this time, I feel sad. I still feel very sad.”

The brazen operation had shocked the world, gave the Palestinian cause a worldwide audience and ushered in a new era of global terrorism. In response, the then Israeli prime minister, Golda Meir, set up a special unit from Israel’s top-secret Mossad agency to hunt down and eliminate all those involved in the massacre.

ABC’s rolling coverage on September 5 was watched by about 900 million people around the world, nearly a quarter of the world’s population. McKay received a congratulatory telegram from Walter Cronkite, the doyen of news anchors.

“That was Jim’s first hint that we had indeed gone a bit beyond the norm,” Mason says. “The more we heard things like that, the more we realised, yeah, this was a special day. In the history of sports television coverage of big events, this is right up there. No question about it.”

Mason’s storied career in sports broadcasting has included seven Olympics, six World Cups, multiple America’s Cup races and Björn Borg v John McEnroe at Wimbledon. He won 26 Emmy awards was inducted into the Sports Broadcasting Hall of Fame. He also struggled with alcoholism for two decades but went to the Betty Ford Center in 1983 and became sober.

“I, like anyone, watch the unfolding of events in our world and feel extremely lucky to have been tangentially involved in the telling of the stories of those events,” he muses. “I leave it to the historians to put meaning and substance and perspective to that. I watch a lot of news and I’m disturbed by some of the things I see; I feel joy at other things I see. But we’re in a complicated world now and so we all have to work harder.”

• September 5 is out in US cinemas on 13 December and in the UK on 6 February