In 1994, against huge odds, two men saved hundreds of Tutsis during the genocide in Rwanda. Finally reunited, they recall the extraordinary story of their first meeting

In a park in London, two men greet each other as old friends. One is grey-haired and American, the other a tall Rwandan in a smart suit. They embrace. The American wipes tears from his eyes. The last time the two men met was in Kigali, the Rwandan capital, in 1994: the year of the genocide in which 800,000 people were killed in 100 days.

The two men, Jean-Francois Gisimba and Carl Wilkens, met a handful of times in that year but in the most extreme of circumstances. Together with Jean-Francois' brother, Damas, they saved more than 400 children and hundreds of adults from the Interahamwe, the Hutu militia intent on eradicating Tutsi "inyenzi" or "cockroaches".

Seventeen years later, the Aegis Trust, which campaigns against genocide, has brought Jean-Francois and Carl back together in the UK. At last, Jean-Francois has the chance to say: "You saved my life but I don't understand why."

Back in 1994, Jean-Francois, then 24, and Damas were running the orphanage their late parents had founded in Kigali in the 1980s. Of mixed Hutu and Tutsi parentage, they were caring for around 60 children of different ethnicities. "We were brought up not to see a difference," Jean-Francois says. Damas ran the orphanage full-time, while Jean-Francois also worked for Radio Rwanda.

On 6 April, a private jet carrying Rwandan President Juvenal Habyarimana was shot down near Kigali airport, triggering the genocide. Government-controlled news organisations began reporting that the Hutu president had been assassinated by Tutsi rebels. Within hours, Kigali was surrounded by roadblocks and the systematic murder of Tutsi families by militia groups began.

Jean-Francois rushed home from the radio station to find hundreds of people gathered at the orphanage, seeking shelter. "They came not because they thought we could save them, but because they didn't want to die alone," he says.

People were hiding in the attic, in the basement and in locked rooms, sick with dysentery and starvation. The brothers kept them alive for months with the help of Red Cross parcels. Because of their father, they had Hutu identity cards, and Damas began to negotiate for the orphanage's survival.

"My brother would go for a beer with the killers," Jean-Francois remembers. "He would say: don't come, don't panic the kids, but he was also protecting the adults inside. He was pretending to be with them."

As the killings continued, the militia members became restless. Armed men began turning up drunk at the orphanage. On one visit they tortured and killed eight people they found hiding on the roof. Then the brothers heard from friends that they planned to kill everyone at the orphanage.

"The day you came was the day the massacre was going to happen," Jean-Francois tells Carl. "There was a knock at the door and I thought: this is it. A boy said, there is a muzungu – a white man – at the door looking for you."

Jean-Francois looks at the man sitting next to him. "It was you in your white Toyota Corolla."

Carl was then the 36-year-old head of Adrai, an Adventist relief organisation working in Rwanda. On 10 April, the UN had evacuated all foreigners from the country, including Carl's wife, parents and three young children.

Carl was the only American who stayed through the genocide. By negotiating with key militia figures including Colonel Tharsisse Renzaho, the prefect of Kigali, he managed to get supplies of water and food through to people in dire need. Renzaho had told him there was an orphanage that needed help.

"I came out and you started telling me: 'I'm bringing water,'" Jean-Francois says. "I wanted you to stop talking. I had the feeling that you did not know what was going on. You just wanted to deliver water and go to the next place. I dragged you to Damas's office.

"I said to you: they are coming in five or 10 minutes to kill all of us. I just wanted you to stay there and witness – so that later you could tell people what had happened."

Carl wanted to leave immediately to fetch help. "I remember standing in the parking lot by my Corolla. You kept on telling me: don't go."

Jean-Francois shakes his head. "We went together slowly up to the car. You were trying to start it. You looked in the mirror and I remember you putting your hands through your hair. You got out again and got on your radio."

As the men stood by the car, dozens of Interahamwe militia began surrounding the orphanage. "The leader said: 'I am coming to take all the Tutsis who are here.'"

"Carl was still on his radio. Then I heard them say: 'We were going to carry out our mission, but the American is there.' The boss said in Kinyarwanda: 'Leave the place, don't do it in front of that man.'"

With Jean-Francois still begging him to stay, Carl left to raise the alarm. When he reached Renzaho's office he found that the prime minister, Jean Kambanda – who would later plead guilty to genocide – was visiting.

"He was one of three people orchestrating the genocide," Carl says. "But what choice did I have? I said: 'There's a massacre about to happen at Gisimba.'

"He talked to his men and said: 'We're aware of this.' He promised me that the orphans would be OK. He shook hands with me."

At the orphanage, Jean-Francois waited. "For three days nothing happened," he says. "Then an army major arrived. Many Interahamwe came behind him. One of the biggest killers – who had killed thousands – was there. 'Inyenzi' he called us – cockroaches."

The major took Jean-Francois aside. "He said to me, 'I am not a killer, I am with you, but you need to tell me the truth.' I decided to trust him. I said, well, the truth is we are hiding many people – more than 400 children, and a big number of adults, widows. I don't even know the number myself.

"He said: 'Be ready to be evacuated.'"

By the next day, more militia had surrounded the orphanage. The Rwandan Patriotic Front (RPF), the Tutsi rebel army fighting their way back into Rwanda, were now close to the capital. "Bombs were landing like rain from the hills," Jean-Francois says. "I thought: now we are going to die.

"The major returned with 12 bodyguards. He said to his men, 'Whoever tries to shoot, you shoot all of them.' If only more soldiers had been like him.

"I thought these were my last moments. There was shooting. They took us to the road. He packed all of us into buses. He had a revolver in his hand and a Kalashnikov on his shoulder. They took us all up to St Michel Cathedral. Two to three days later the RPF took the area and we were safe."

More than 17 years later, Carl and Jean-Francois have met again because the Gisimba orphanage (still run by Jean-Francois and Damas) needs money. Next week is the 25th anniversary of the orphanage's foundation. "We want it to have a future," Jean-Francois says.

In London, the American turns to the Rwandan and says: "I never knew if it was the right decision to leave you at the orphanage."

"It was the right decision," Jean-Francois replies. "But what about my question – why did you help us?"

Carl talks about not abandoning his Rwandan staff and friends, but Jean-Francois is shaking his head. "You were on the other side of the city so why cross through all those roadblocks, bombs and bullets to get to the orphanage?"

Carl looks at him as if he should know. Jean-Francois, after all, is a man who let hundreds shelter in the orphanage knowing it meant almost certain death. "Why did you help those people?" he asks.

Jean-Francois looks at him with incredulity. "How would we turn people away? We were taught by our parents that we should respect other people's lives. If you tell people to get away you are an animal not a human being."

And so somehow he himself answers the question he has been waiting 17 years to ask.

For further information on the Gisimba Orphanage, and details about how to support it, go to www.aegistrust.org