Sabra and Shatila were the scene of war crimes. In September of 1982, Israel’s Lebanese Christian allies – watched by Israeli troops who had surrounded the Palestinian refugee camps – massacred up to 1,700 civilians. It was a place of horror and, much later, of memorial. The mass grave still lies beneath a tide of mud behind a stand of trees where Syrian refugees sell cheap shirts and DVDs. But the names of Sabra and Shatila are today associated with a shame which no one could have imagined 34 years ago .

Drug-dealing has now tainted the camps – by the Syrians more than the Palestinians – and there have been murders and, most tragic of all, prostitution. No one in Sabra and Shatila hides their sorrow. The massacre, the survivors’ grief, the years of misery and the siege by Shia Amal militiamen – who killed more Palestinians than the Israelis – did not break the Palestinians, but it doesn’t take long today to understand the depth of their despair.

“What do you expect when a refugee population lives in this poverty and when they have less and less money?” one of the local camp leaders asked as we walked the narrow alleyways – so narrow that your shoulders rub the slum walls on each side. “The Lebanese do not allow Palestinians to work outside the camps, the UN relief money is getting less and less, some have families abroad who send money to them. Others do not.”

The man was right. Where refugees live, the mafia arrives, the people-smugglers; the cruel and the rapacious thrive amid sorrow, just as they did in Bosnia after the war of 1992-95. The Palestinians first arrived in Sabra and Shatila in 1948. It took almost 70 years and the 1982 massacre before the shame of drugs and prostitution touched this place. Nor is it on a scale to attract attention. Only a very few Palestinian women have left the camps – they must leave for the sake of family honour – and moved elsewhere in Lebanon, to Jounieh north of Beirut, according to a political official in the camps.

As a witness to the massacre of 1982, I went back often to this place of memories and ghosts, to talk to the few survivors. Sabra and Shatila are scarcely two miles from my Beirut home. There were five thousand Palestinians in the camps in 1982, perhaps only 3,000 today. But an article in one of the local Beirut papers had caught my attention. A middle-aged Palestinian, it reported, had been shot dead by two Islamists on a motorcycle. Did this mean that the Isis cult had infected even Sabra and Shatila? In which case, Isis was in Beirut.

The moment I arrived, I was told that no, the newspaper story was untrue. The Lebanese government had claimed the murderers were Islamists in order to enhance their own prestige for taking one of the killers into custody. Arab governments line up to tell the world these days that they are fighting Isis – in the hope the West will give their armies more guns. But this story, too, I discovered, was untrue.

Ahmad Hazineh was a good and decent man. No criminal. He did indeed help supply his people with clean water and electricity for a pitifully small sum, but he fell foul of the local mafia who wanted him to collect more cash from the Palestinians. He refused – and so they murdered him.

But when Suheil Natour of the Democratic Front and I began to prowl these foul-smelling streets, we were faced with anger of the rawest kind. One middle-aged man saw my camera and burst out from his iron door, his face dark and lined.

“How dare you people take pictures of us?” he screamed, another man beside him, shaking in fury. “How dare you humiliate us? Do you know this place is filled with mice and huge rats and we live in this shit and sewage and stench and there are thieves and drugs and prostitution?” He actually used the word “prostitution”. He understood the shame. He was shouting so loudly now that Suheil tried to restrain him and put his arm on the man’s shoulder. He threw it off.

But Suheil had noticed something else. A poster dedicated to a Palestinian “martyr”, a newly murdered man, Ahmad Hazineh, also known as Abu Wassem, whose home – by extraordinary coincidence – was next to us, just beside the shouting man and his companion. And there stood in the doorway a young woman, listening sadly to this fit of screaming next door.

“People here are very angry,” she said, smiling. “Yes, Ahmad Hazineh was my father. He died on 28 January, just a month ago. He was a good man. He helped everyone. The mafia killed him. Yes, there are drugs and prostitution in the camps. But my father looked after my siblings and myself and he told me every day that I must be educated. He sent me to act in theatre in the UK. I have been to London and Newcastle.”

And Nirmeen Hazineh, dark-haired and still smiling, talked again of her love for her father, and she saw how the names of “London” and “Newcastle” – where, more than half a century ago, I was a cub reporter on the local paper – touched us. It was as if a beautiful light had suddenly been switched on amid the vile slums of Sabra and Shatila, brighter than any lamp her father could have lit with his electricity supply.

Nirmeen’s English was impeccable. She talked of her hope for better days. There was still some justice, she said. One of her father’s alleged murderers had been arrested, a man who was now in Roumieh prison north of Beirut.