Another war on terror. Another proxy army. Another mysterious massacre. And now, after 19 years, perhaps the truth at last...

Sana Sersawi speaks carefully, loudly but slowly, as she recalls the chaotic, dangerous, desperately tragic events that overwhelmed her just over 19 years ago, on 18 September 1982. As one of the survivors prepared to testify against the Israeli prime minister Ariel Sharon – who was then Israel's defence minister – she stops to search her memory when she confronts the most terrible moments of her life. "The Lebanese Forces militia [Phalangists] had taken us from our homes and marched us up to the entrance to the camp where a large hole had been dug in the earth. The men were told to get into it. Then the militiamen shot a Palestinian. The women and children had climbed over bodies to reach this spot, but we were truly shocked by seeing this man killed in front of us and there was a roar of shouting and screams from the women. That's when we heard the Israelis on loudspeakers shouting, 'Give us the men, give us the men.' We thought, 'Thank God, they will save us.'" It was to prove a cruelly false hope.

Mrs Sersawi, three months pregnant, saw her husband Hassan, 30, and her Egyptian brother-in-law Faraj el-Sayed Ahmed standing in the crowd of men. "We were told to walk up the road towards the Kuwaiti embassy, the women and children in front, the men behind. We had been separated. There were Phalangist militiamen and Israeli soldiers walking alongside us. I could still see Hassan and Faraj. It was like a parade. There were several hundred of us. When we got to the Cité Sportif, the Israelis put us women in a big concrete room and the men were taken to another side of the stadium. There were a lot of men from the camp and I could no longer see my husband. The Israelis went round saying 'Sit, sit.' It was 11am. An hour later, we were told to leave. But we stood around outside amid the Israeli soldiers, waiting for our men."

Sana Sersawi waited in the bright, sweltering sun for Hassan and Faraj to emerge. "Some men came out, none of them younger than 40, and they told us to be patient, that hundreds of men were still inside. Then about 4pm, an Israeli officer came out. He was wearing dark glasses and said in Arabic: 'What are you all waiting for?' He said there was nobody left, that everyone had gone. There were Israeli trucks moving out with tarpaulin over them. We couldn't see inside. And there were jeeps and tanks and a bulldozer making a lot of noise. We stayed there as it got dark and the Israelis appeared to be leaving and we were very nervous. But then when the Israelis had moved away, we went inside. And there was no one there. Nobody. I had been only three years married. I never saw my husband again."

Today, a Belgian appeals court will begin a hearing to decide if Prime Minister Sharon should be prosecuted for the massacre of Palestinian civilians at the Sabra and Chatila refugee camps in Beirut in 1982. (Belgian laws allow courts to try foreigners for war crimes committed on foreign soil.) In working on this case, the prosecution believes that it has discovered shocking new evidence of Israel's involvement.

The evidence centres on the Camille Chamoun Sports Stadium – the "Cité Sportif". Only two miles from Beirut airport, the damaged stadium was a natural holding centre for prisoners. It had been an ammunition dump for Yasser Arafat's PLO and repeatedly bombed by Israeli jets during the 1982 siege of Beirut so that its giant, smashed exterior looked like a nightmare denture. The Palestinians had earlier mined its cavernous interior, but its vast, underground storage space and athletics changing-rooms remained intact. It was a familiar landmark to all of us who lived in Beirut. At mid-morning on 18 September 1982 – about the time Sana Sersawi says she was brought to the stadium – I saw hundreds of Palestinian and Lebanese prisoners, probably well over 1,000, sitting in its gloomy, dark interior, squatting in the dust, watched over by Israeli soldiers and plain-clothes Shin Beth (Israeli secret service) agents and men who I suspected were Lebanese collaborators. The men sat in silence, obviously in fear. From time to time, I noted, a few were taken away. They were put into Israeli army trucks or jeeps or Phalangist vehicles – for further "interrogation".

Nor did I doubt this. A few hundred metres away, inside the Sabra and Chatila Palestinian refugee camps, up to 600 massacre victims rotted in the sun, the stench of decomposition drifting over the prisoners and their captors alike. It was suffocatingly hot. Loren Jenkins of The Washington Post, Paul Eedle of Reuters and I had only got into the cells because the Israelis assumed – given our Western appearance – that we must have been members of Shin Beth. Many of the prisoners had their heads bowed. But Israel's Phalangist militiamen – still raging at the murder of their leader and president elect Bashir Gemayel – had been withdrawn from the camps, their slaughter over, and at least the Israeli army was now in charge. So what did these men have to fear?

Looking back – and listening to Sana Sersawi today – I shudder now at our innocence. My notes of the time, subsequently written into a book about Israel's 1982 invasion and its war with the PLO, contain some ominous clues. We found a Lebanese employee of Reuters, Abdullah Mattar, among the prisoners and obtained his release, Paul leading him away with his arm around the man's shoulders. "They take us away, one by one, for interrogation," one of the prisoners muttered to me. "They are Haddad [Christian militia] men. Usually they bring the people back after interrogation, but not always. Sometimes the people do not return them." Then an Israeli officer ordered me to leave. Why couldn't the prisoners talk to me, I asked? "They can talk if they want," he replied. "But they have nothing to say."

All the Israelis knew what had happened inside the camps. The smell of the corpses was now overpowering. Outside, a Phalangist jeep with the words "Military Police" painted on it – if so exotic an institution could be associated with this gang of murderers – drove by. A few television crews had turned up. One filmed the Lebanese Christian militiamen outside the Cité Sportif. He also filmed a woman pleading to an Israeli army colonel called "Yahya" for the release of her husband. (The colonel has now been positively identified by The Independent. Today, he is a general in the Israeli army.)

Along the main road opposite the stadium there was a line of Israeli Merkava tanks, their crews sitting on the turrets, smoking, watching the men being led from the stadium in ones or twos, some being set free, others being led away by Shin Beth men or by Lebanese men in drab khaki overalls. All these soldiers knew what had happened inside the camps. One of the members of the tank crews, Lt Avi Grabovsky – he was later to testify to the Israeli Kahan commission – had even witnessed the murder of several civilians the previous day and had been told not to "interfere".

And in the days that followed, strange reports reached us. A girl had been dragged from a car in Damour by Phalangist militiamen and taken away, despite her appeals to a nearby Israeli soldier. Then the cleaning lady of a Lebanese woman who worked for a US television chain complained bitterly that Israelis had arrested her husband. He was never seen again. There were other vague rumours of "disappeared" people.

I wrote in my notes at the time that "even after Chatila, Israel's 'terrorist' enemies were being liquidated in West Beirut". But I had not directly associated this dark conviction with the Cité Sportif. I had not even reflected on the fearful precedents of a sports stadium in time of war. Hadn't there been a sports stadium in Santiago a few years before, packed with prisoners after Pinochet's coup d'etat, a stadium from which many prisoners never returned?

Among the testimonies gathered by lawyers seeking to indict Ariel Sharon for war crimes is that of Wadha al-Sabeq. On Friday, 17 September 1982, she said, while the massacre was still (unknown to her) underway inside Sabra and Chatila, she was in her home with her family in Bir Hassan, just opposite the camps. "Neighbours came and said the Israelis wanted to stamp our ID cards, so we went downstairs and we saw both Israelis and Lebanese Forces [Phalangists] on the road. The men were separated from the women." This separation – with its awful shadow of similar separations at Srebrenica during the Bosnian war – were a common feature of these mass arrests. "We were told to go to the Cité Sportif. The men stayed put." Among the men were Wadha's two sons, 19-year-old Mohamed and 16-year-old Ali and her brother Mohamed. "We went to the Cité Sportif, as the Israelis told us," she says. "I never saw my sons or brother again."

The survivors tell distressingly similar stories. Bahija Zrein says she was ordered by an Israeli patrol to go to the Cité Sportif and the men with her, including her 22-year-old brother, were taken away. Some militiamen – watched by the Israelis – loaded him into a car, blindfolded, she claims. "That's how he disappeared," she says in her official testimony, "and I have never seen him again since."

It was only a few days afterwards that we journalists began to notice a discrepancy in the figures of dead. While up to 600 bodies had been found inside Sabra and Chatila, 1,800 civilians had been reported as "missing". We assumed – how easy assumptions are in war – that they had been killed in the three days between 16 September 1982 and the withdrawal of the Phalangist killers on the 18th, that their corpses had been secretly buried outside the camp. Beneath the golf course, we suspected. The idea that many of these young people had been murdered outside the camps or after the 18th, that the killings were still going on while we walked through the camps, never occurred to us.

Why did we not think of this at the time? The following year, the Israeli Kahan commission published its report, condemning Sharon but ending its own inquiry of the atrocity on 18 September, with just a one-line hint – unexplained – that several hundred people may have "disappeared" at about the same time. The commission interviewed no Palestinian survivors but it was allowed to become the narrative of history. The idea that the Israelis went on handing over prisoners to their bloodthirsty militia allies never occurred to us. The Palestinians of Sabra and Chatila are now giving evidence that this is exactly what happened. One man, Abdel Nasser Alameh, believes his brother Ali was handed to the Phalange on the morning of the 18th. A Palestinian Christian woman called Milaneh Boutros has recorded how, in a truck-load of women and children, she was taken from the camps to the Christian town of Bikfaya, the home of the newly assassinated Christian president-elect Bashir Gemayel, where a grief-stricken Christian woman ordered the execution of a 13-year-old boy in the truck. He was shot. The truck must have passed at least four Israeli checkpoints on its way to Bikfaya. And heaven spare me, I realise now that I had even met the woman who ordered the boy's execution.

Even before the slaughter inside the camps had ended, Shahira Abu Rudeina says she was taken to the Cité Sportif where, in one of the underground "holding centres", she saw a retarded man, watched by Israeli soldiers, burying bodies in a pit. Her evidence might be rejected were it not for the fact that she also expressed her gratitude for an Israeli soldier – inside the Chatila camp, against all the evidence given by the Israelis – who prevented the murder of her daughters by the Phalange.

Long after the war, the ruins of the Cité Sportif were torn down and a brand new marble stadium was built in its place, partly by the British. Pavarotti has sung there. But the testimony of what may lie beneath its foundations – and its frightful implications – might give Ariel Sharon further reason to fear an indictment.