Two police vans waited expectantly near the front entrance. Officers patrolled the pavements while suited security men with ear pieces stood stern-faced, casting suspicious looks at those approaching. The location in east London had not been disclosed until that morning but no chances were being taken.

It was not for a visiting dignitary or even an embassy of a country in conflict that all this was deemed necessary but the Nova exhibition, a commemoration of the 378 people massacred at a music festival on 7 October along with the 44 taken as hostages and the 19 of those who died in Hamas captivity.

When the exhibition had travelled to New York, hundreds of people had turned up in Lower Manhattan to protest against the conduct of Israel since the 7 October attack, some of whom claimed the show was a piece of political propaganda.

Elkana Bohbot, a co-organiser of the 2023 music festival, who spent 738 days as a hostage in Gaza of which 690 were in a tunnel, said he had only one request to those who might turn up to demonstrate in London: “Come in for one minute. Not an hour but just one minute. Come inside. That’s it.”

London is the 10th city to host the immersive reminder of this part of the worst atrocity committed against Jews since the Holocaust. There is a room of shoes belonging to those who fled, evoking memories of the spectacles, hair and footwear that helped evidence the crimes of the concentration camps. But the horror at Nova is perhaps among the most documented of our times. The exhibition in Shoreditch, which opens to the public on Wednesday, seeks to use that which was caught in technicolour, via the phones of the victims and body cameras of the protagonists, to challenge “with their own eyes” those who deny its gravity, said Bohbot, 36, whose pallor perhaps offers evidence aplenty of the continued trauma that haunts his nights.

Visitors to the six-week exhibition are first shown a three-minute film of partygoers speaking of the bliss of the event, and the beauty of the sunrise that morning as they continued to dance. That ends with footage capturing the moment that the DJ on the main stage was told that the music had to stop. “Red alert, red alert,” the crowd were told.

The next room in the exhibition – dark, noisy and chaotic – is scattered with the belongings of the participants along with other significant pieces from the crime scene. There are burned-out cars and shot-through toilet cubicles next to the pro-cam footage showing how it came about. There is audio of those who found themselves cowering under bushes or forced into the horribly evocative marches of tens of miles to relative safety. A recording also captures the moment that one of the Hamas attackers boasted to his father that he had killed “10 Jews with my own hands” and was calling from the “phone of a Jew” he had killed along with her husband.

Another exhibit is the CCTV positioned outside one of the bomb shelters near the festival where young men and women hid for their lives. Grenades can be seen thrown in by the terrorist – and chucked out just as quickly by Aner Shapiro, 22, a British-Israeli citizen and off-duty Israeli soldier who had simply come to dance with friends.

His parents Moshe, 55, and Shira, 50, said that they had been able to account for every moment of the last 30 minutes of their son’s life thanks to the first-hand accounts, phone footage and CCTV. There were 27 people in the shelter, designed for eight. “He told them: ‘My name is Aner Shapiro, I’m a soldier. I have to tell you, there’s a war now, a big war. Don’t be afraid. You’ll be OK. I will protect you,’” said Shira, who was born in Oxford. Shapiro is believed to have thrown out as many 11 grenades before an rocket-propelled grenade was used on him followed by more grenades. He died after taking a shot to the head. He had told those behind him to try to follow his lead should he fall. They did until the Hamas attackers stormed in. Five of the 16 inside were taken hostage. One was shot there and then. Three later returned alive from Gaza.

The protest outside the event in New York was a “manifestation of how important it is to do this exhibition over and over and in more and more places,” said Aner’s father. “They don’t want to know. But it’s not that they cannot learn about what happened.”

Lisa and Michael Marlowe, from north London, last spoke to their son, Jake, 26, at 4.30am UK time on 7 October. He was an unarmed security guard at the festival. “Oh he’ll be asking for money again,” said Michael, 64, of his thoughts on receiving the early morning call. “He was just saying: ‘I love you. And I’ll keep in touch. There’s a lot of commotion going on, there are paragliders in the air. I’ll call you back when it’s all calmed down.’” Jake never did call back. “It is important for everyone to see the exhibition,” said Michael, who had to identify his son in a morgue in Israel. “We are not lying.”