Near the old civil-war front line in the centre of Beirut stands a large digital clock with blood-red numbers. It has almost reached the neat, round figure of 1,500 and represents the days since Rafiq Hariri was murdered. You still hear people in Lebanon asking for "haqiqa" – "the truth"; my driver Abed even has a slim, black sticker tied to the mirror of our car with the word in Arabic script. The trouble is that as that figure on the digital clock goes on climbing, a lot of Lebanese are beginning to doubt they will ever know who murdered the billionaire and former prime minister – along with 21 others – on the Beirut Corniche on 14 February 2005. This St Valentine's Day massacre was caused by an estimated 1,700kg of explosives, but despite a massive United Nations inquiry involving Irish police officers, judges from Germany, Belgium and Canada, and the setting up of an entire tribunal headquarters in The Hague, no one has been charged.

Four men are still in the grim prison at Roumieh, north of Beirut, on suspicion of involvement in the crime; they are – or were – senior officers in the Lebanese security apparatus whose first loyalty was to Damascus rather than Beirut. In the aftermath of the assassination, everyone from the then-president of France, Jacques Chirac, to the leader of the Lebanese Druze community Walid Jumblatt saw the hand of Syria. Who else could plan such a massive explosion in one of the most supposedly secure parts of the Lebanese capital? Hadn't the Syrian president Bashar al-Assad expressed his contempt for Hariri? And weren't the string of assassination victims that followed Hariri's death all opposed to Syria? Sister Syria was the butler in the Lebanese manor house, and it was the butler what did it.

Perhaps. But now that Barack Obama is arriving in the White House with a mission to start a "dialogue" with Syria – and since America desperately needs Syria's help in preventing insurgents from attacking its troops in Iraq – it's not hard to imagine what form this "dialogue" will take. Yes, the Americans need help. Yes, Damascus will understand the need for a less confrontational approach to the Arab world from a US administration. And yes, the Americans would like Syria to break off its relations with Iran – some hope! – and with Hamas. But, hem-hem, there may be a little matter of the Hariri tribunal to be discussed before the "dialogue" begins.

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Hariri was always a problem for Syria. While a friend of the Syrian regime – he built the presidential palace in Damascus as a gift – and a citizen of Saudi Arabia, to whom Syria has always shown respect, the Syrians always suspected Hariri wanted to restore Lebanon's full sovereignty and free it from the overlordship of Damascus. Fearful of a pro-Israeli regime in Beirut – which briefly occurred in 1982 after Israel's massive invasion – Syria felt comfortable only when its own allies were in power in Lebanon. Hence it "fixed" the Beirut parliament to contain more friends than enemies and ensured the Lebanese president would always show fealty to Damascus. Hence Hariri's dangerous position.

Assad never believed there would be a UN inquiry into Hariri's murder and it was only after I revealed in the Independent that there would be, that an astonished President Hosni Mubarak of Egypt rushed to his presidential jet and flew to Syria to warn Assad that he might be in very hot water indeed. The first UN team was led by Irish Deputy Garda Commissioner Peter Fitzgerald, who discovered that the wreckage of Hariri's six-car motorcade had – incredibly – been moved from the crime scene at midnight on the day of the killings and other materials not associated with the bomb placed in the massive crater. The man responsible for doing so was General Ali al-Hajj, director general of the (then Syrian-dominated) Lebanese Internal Security Forces and one of the four men now locked up in Roumieh awaiting his day in court. If there is a court.

Al-Hajj used to work for Hariri, as his bodyguard, but was removed from his personal retinue when Hariri discovered he was also working for Syrian intelligence. He actually ' had the nerve to turn up at the Hariri family palace in Beirut's Koreitem district to offer his condolences on the day of the murder. I reported that night that one of Hariri's young relatives had told him: "Your place is not here." She turned up at my home with some student friends 24 hours later to say I had misquoted her. "What I said was, 'Your place is not here – you dog!'" Well, I tried. Also in Roumieh is the former head of Lebanese military intelligence General Raymond Azar, Brigadier General Mustafa Hamdan (commander of the Presidential Guards Brigade), and the sinister figure of a certain Jamil Sayed. I received a sharp example of where power lies in Beirut when I appealed to Hariri some years before his death to un-ban my book on the Lebanese civil war. Hariri said it was not "the right time" to risk offending Syria. But – strange as the ironies are in Beirut – the ban was immediately lifted after eight years of censorship following a one-minute phone call to Sayed. Sayed was director-general of the General Security Department of the Lebanese interior ministry; not a man you would choose to argue with.

But nor was Hariri. Although he was an immensely wealthy philanthropist – he sent my driver Abed's son through university (he was at Essex), along with thousands of other Lebanese students – he could be a ruthless businessman. He built hospitals and even tried to rebuild Beirut in the middle of the 1975-1990 civil war – then rebuilt it again after. But bankers feared his power, especially when he began buying up square miles of real estate. I once asked if he believed in God, and he said he did (which I thought was true) but when I asked him how much of Lebanon he had bought, he said he didn't know (which I think was untrue). A Lebanese businessman with whom he was involved in a ferocious row was wounded by the bomb that killed Hariri and thought at first that the bomb had been set off by Hariri to kill him.

But how was the bomb constructed? The second UN team to arrive in Lebanon believed it was in a truck driven by a suicide bomber. Indeed, within hours of the murder the pro-Syrian information minister blurted out that it had been "a martyrdom mission", which could have been a giveaway. Surely the minister regarded Hariri as the "martyr"? Or did he not?

The killings were followed by a series of macabre assassinations, which showed that the killers were still operational: the writer and journalist Samir Kassir blown up in his car outside his Beirut home; the politicians George Hawi, also blown up in his car in west Beirut, and Walid Eido (another car bomb, outside his favourite watering hole); the newspaper editor Gibran Tueni, atomised by a car bomb on a lonely pine-lined road in east Beirut; the MP Pierre Gemayel. All these men had come out firmly against Syria's involvement in Lebanon – Kassir had apparently been threatened by Sayed over the telephone when Hariri was still alive.

Then Samir Shehade, an army officer investigating the thousands of phone calls made in the hour of Hariri's murder – he was the Lebanese military's top cell-phone expert – was also killed by car bomb. One of the calls he was investigating was allegedly made to the presidential palace where Émile Lahoud, a Damascus protégé, still ruled. An official who took the call was told Hariri was dead. He should have responded with shock, one might think. What he asked was: "Are you sure?"

Syria, it should be said, has always denied the killings. When I asked Syria's foreign minister in Paris who killed Hariri, he produced all the money in his pocket, put it on the table in the lobby of his palatial hotel and told me: "If you can tell me who killed Hariri, you can take all that!" The American journalist Seymour Hersh was with Assad when he received news of Hariri's murder. Hersh told me that although Assad had been deeply critical of Hariri and regarded him as a corrupt man, he appeared astonished at the news. Yet the Druze leader Jumblatt, among the world's greatest nihilists – I should explain that he rather likes this description – had no doubt that Syria was to blame; indeed that Syria had murdered his father Kamal because he "refused... Syria's Anschluss".

Jumblatt was at his Beirut home when the explosion that killed Hariri thundered across the city. "I knew at once that it must be Hariri," he told me. "It was either going to be me or Hariri and it wasn't me. I felt I should go upstairs and put on a black tie, but that this was a way of killing Hariri and I hesitated. Then I called his house at Koreitem and they said that all his mobile phones were dead; then I knew, and went upstairs and put on a black tie. At the American University Hospital, I knew one of the people in the morgue and he told me that Hariri was gone. So I got one of his sons into the car with me and told him, 'The news is not good.'"

The slaughter led to a UN Security Council resolution that demanded – and got – the withdrawal of Syria's 14,000 troops from Lebanon. They had first been sent to Beirut with US President Jimmy Carter's approval to stop the civil war in 1976 – they failed, of course, but stayed on to police the country for another 29 years, with men such as al-Hajj and Sayed working for them. After Hariri's murder the UN inquiries blundered on, sometimes arresting the wrong men and constantly promising "the truth" without providing it. One UN report was released in New York with the names of Syrian security apparatchiks in the text. It was hurriedly censored by UN secretary-general Kofi Annan – the first indication that Sister Syria might, after all, escape unscathed.

Jumblatt himself was so worried that the UN tribunal might be abandoned that he set off to Washington and secured a 35-minute interview with George W Bush – only 10 minutes less than the Israeli prime minister Ehud Olmert received – and spent even longer with the head of the CIA. This was pretty suicidal stuff, an anti-Syrian Lebanese politician talking to the neo-conservatives of the US about the need for a tribunal to indict Syria. President Chirac of France had joined the Americans in sponsoring the Security Council military-withdrawal call to Damascus, although the Hariri-Chirac friendship was said to be based on business as much as mutual admiration. (When in Paris, Hariri lived in the old home of Gustave Eiffel and was widely believed to have helped fund Chirac's presidential campaigns – a subject Chirac avoided on his visits to Beirut. Chirac, who had wanted to be friends with Bashar, felt personally betrayed by Hariri's murder.)

But Nicolas Sarkozy is no Chirac. He wanted to restore France's relations with Syria – not to mention Syria's relations with the French Total oil company – and invited Bashar to this year's Bastille Day bash on the Champs-Élysées. Sarkozy was duly invited to Damascus, then popped across to Beirut to reassure the Lebanese that France was their best friend. There is a suspicion in the Lebanese capital that all French presidents want, in their heart of hearts, to restore France's prewar mandates over Lebanon and Syria – General Henri Gouraud created Lebanon out of Syria against the wishes of the country's Muslim population and a young Captain Charles de Gaulle served that mandate in a villa which Hariri later restored. It was a miserable story and one which Sarkozy has continued by supporting the Doha peace agreement, which effectively gave the pro-Syrian opposition in Beirut veto powers over cabinet decisions. In other words, Syrian hegemony returned to Lebanon without its army.

All this while, the Hizballah militia – or "resistance army", as it likes to call itself – remained a faithful friend (or servant) of Syria. After Hariri's murder, its general-secretary, Sayed Hassan Nasrallah, said that he sometimes held secret meetings with Hariri to discuss the future of Lebanon. But I remember Hariri expressing his anger at Nasrallah when he discovered that the Hizballah intended to bury some of their south Lebanese "martyrs" in front of Beirut International Airport – a step unlikely to encourage more tourists or businessmen to the country Hariri was trying to rebuild.

In Beirut, Hariri's memory is safeguarded by his anti-Syrian son Saad. But Saad's power was brutally cut down when his ragtag militia failed to halt a virtual Hizballah takeover of west Beirut in which they seized Saad's party headquarters and closed down his television station. Jumblatt had warned Saad not to collect a militia because the Hizballah could overwhelm it. But Saad went ahead. He was wrong. Jumblatt was right.

And so Rafiq Hariri's reputation has been diminished by his son's failure. The money is still intact, of course: the Hariris own parts of Houston, Texas, as well as Beirut and Paris; and honest reflection by Beirut's bankers – who are not always very honest – suggests that Hariri's rise to financial prominence during the Syrian presence in Lebanon encouraged widespread corruption. At one point, he ran two governments; a dull, official one that reflected Syria's views and a "shadow" government of technocrats paid by Hariri himself, which actually managed the country. When he first became prime minister in 1992, Hariri was worth about $1bn. But he was primary shareholder in Solidere, the company that built (and is still building) downtown Beirut, which left him worth $16bn at his death, listed among Forbes' top 100 wealthiest men and women in the world and the fourth-richest politician. Solidere appropriated the wrecked centre of Beirut and compensated property owners with shares in the company that were sometimes worth 15 per cent of the value. Money would be dispatched to government ministers to "minimize the inconvenience" of their offices – to use the words of Thomas Cromwell in Robert Bolt's A Man for All Seasons. Indeed, there was something of Henry VIII in Hariri, a man who – in the words of a colleague reflecting on his business activities – was overweight and ruthless but quite prepared to smile like a cat that had just eaten the family budgerigar.

Hence he became known as "Mr Lebanon", a dangerous title in a land so soaked in blood. The integrity of Lebanon's internal quarrel remains intact despite its people's intelligence and charm and kindness. And the Hizballah have shown a side to this country that had never before been witnessed in Lebanon. Seeing themselves as warriors rather than mere gunmen, they fought the Israeli army to a standstill in the summer of 2006 and may do the same this year when a new right-wing Israeli government might be provoked by Iran's most valuable ally in Lebanon.

What would Hariri have said? He always believed Iran would try to play a major role in Lebanon's internal politics. The Iranians became convinced that he was killed by an off-shoot of al-Qa'ida from Iraq after holding a secret meeting with Iraq's acting prime minister in Beirut. Other stories suggested something had gone wrong in a Saudi-Russian arms deal which Hariri had negotiated. Meanwhile, the UN tribunal has been given a home in The Hague – in a former Dutch intelligence headquarters – so that its work can begin in February. Or March. Or sometime this year. Even in late 2007, Serge Brammertz, who was then in charge of the inquiry, was talking about the "extreme delicacy" of his work because his investigation was "approaching a sensitive and complicated phase". Ho hum, said the Lebanese. They knew what that meant. Then in mid-December last year, the Canadian prosecutor Daniel Bellemare – the latest in a bewildering range of UN officials to become involved – announced that despite "difficulties", the case of Hariri's murder could be solved. "Absolutely!" he announced with Blair-like assurance. The Lebanese were not assured.

Will there ever be a trial? And even if there is, will it merely be a UN façade – in which nameless murderers will be excoriated, Syria absolved from the crime and Hariri's death remain unavenged? Will lawyers for the four Lebanese already locked up succeed in their petitions to obtain at least their limited freedom? Not once in more than three decades has a single political murder in Lebanon ever been solved. Besides, just as the 2006 Israeli-Hizballah war overwhelmed all interest in the UN investigation, there will be more crises and, unfortunately, more violent conflicts in Lebanon to give Hariri's murder yet further historical distance and – dare one say it – political irrelevancy. The Lebanese would not agree with this. But the world might.

A few metres from the spot where he died, a larger-than-life statue of Rafiq Hariri now stands on a plinth opposite the sea. It's a good likeness, the overweight ex-prime minister with his hands shoved into his pockets, his trousers curling slightly over his shoes, a proud, immensely wealthy, rather frightening man who stares out over the city he rebuilt. Abed still keeps his label over the mirror with "the truth" printed on it. But all of us in Beirut are beginning to wonder if we will ever know what that is.