By Jeremy Bowen
Middle East editor, BBC News
No-one except the gunmen and the men who paid them knows who killed Pierre Gemayel.
They operated in daylight, and did not bother to cover their faces.
They did not use a bomb, unlike the killers of the five other prominent anti-Syrian figures who have been assassinated here since the beginning of last year.
Syria rejects accusations it was behind Pierre Gemayel's murder
Instead, they crashed their cars into his, leapt out and opened fire on Mr Gemayel and his two bodyguards with their machine guns.
It was like a hit in a Martin Scorsese film about the Mafia - except that it was real, it was deadly serious and it
sent shockwaves across Beirut and Lebanon and out into the wider world.
It inflamed the tensions between Lebanon's different communities and it opened up old scar tissue left from the 15 years of civil war in the seventies and eighties.
Pierre Gemayel, a rising young politician from a prominent Lebanese Christian family, was killed along with one of the guards.
But his other bodyguard survived, along with a local shopkeeper who saw the killing.
The gunmen noticed that he was watching, and shot him too, but they did not manage to kill him.
It is possible to make an argument that President Assad has enemies who might want to discredit him at the moment when foreign leaders were remembering they had his phone number
Those two witnesses might have some information for the police.
But without any hard evidence as yet, people in Lebanon are speculating constantly about who might have wanted to kill Pierre Gemayel.
The assumption in the crowd of hundreds of thousands of people who gathered for his funeral and for the political rally that was held alongside it in downtown Beirut on Thursday was that Syria ordered the killing.
Valentine's Day killing
Lebanese politics is currently paralysed by a split over Syria's role in the country.
The government here is controlled by an anti-Syrian coalition that came together after the former Prime Minister, Rafik Hariri, died in the first of the series of assassinations, on St Valentine's Day in 2005.
It calls itself the 14th March Movement, after the huge demonstration a month later which blamed Syria for the killing and kicked off a wave of international pressure that forced Syria to pull its troops out of Lebanon.
Mr Gemayel's murder was the latest in a series of assassinations
The people in the 14th March Movement, like the late Pierre Gemayel, believe that Syria's control of Lebanon over more than 20 years was a disaster and that it should be stripped of the power it still has here.
The split is deep because the other side of Lebanese politics, led by Hezbollah and its leader Hassan Nasrallah, sees Syria - and Iran too for that matter - as natural allies for Lebanon.
The pro-Syria camp also contains Michel Aoun, an important Christian leader.
He is an ex-general who was president at the end of the civil war, when he tried to fight the Syrians.
Syria was linked to the Hariri assassination by a UN investigation that is still going on.
The anti-Syrian government in Beirut is in the process of setting up an international tribunal to prosecute Mr Hariri's killers.
The assumption on their side is that Damascus is trying to topple their government to torpedo the tribunal, which could try to take action against senior Syrian officials.
They also suspect that Syria wants to cause more sectarian tension and even civil strife so that it would be able, as it has done in the past, to present itself as the only country capable of restoring order.
But others, and not just those who are visceral supporters of Damascus, are asking what interest Bashar al-Assad, the Syrian president would have in killing Pierre Gemayel.
Not so long ago, there was talk in Washington of trying to force regime change in Syria.
But in the last few months the conversation about Syria shifted; Syria was being seen as a force for stability.
The British Prime Minister, Tony Blair, sent a top adviser to Damascus for talks.
On the morning of the Gemayel assassination, Syria announced it was re-establishing diplomatic relations with the American-backed government in Iraq, signalling that it wanted to be in the Middle East diplomatic game.
Bashar al-Assad was looking as if he was in a good position.
His friends in Hezbollah gave Israel a bloody nose in the summer.
Relations with Iran are strong and Western countries seemed to be competing for his attention.
Syria has acted in ways that appeared to be against its own interests in the past.
It is possible to speculate that President Assad and his advisers believed that the Americans were so desperate to get some Arab help in Iraq that they would look away if Syria started getting up to its old tricks in Lebanon.
There are fears the killing will deepen sectarian fault lines
But, until the assassination, many new options seemed to be opening up for President Assad.
Would he really have wanted to close them down? Would it really have been in his best interests to order a political killing in Beirut for which Syria was always likely to get blamed?
What if the order came from Syria but not from the desk of the president? Again, it is possible to make an argument that President Assad has enemies who might want to discredit him at the moment when foreign leaders were remembering they had his phone number.
But if not Syria, who? In the last few days in Beirut I have had heard theories linking Israel, the United States and other Lebanese Christian leaders with Mr Gemayel's assassination, for a variety of reasons - to remove a rival in the case of the Christians, to spread confusion and dismay for the others.
No-one has produced any evidence for any of the theories that are flying around.
But, in the absence of hard facts, the theories will keep circulating, at a faster and faster rate.
None of the killers in any of the assassinations in the last almost two years has been prosecuted.
No-one is holding their breath for a police announcement that they have found the men who emptied the magazines of the weapons into Pierre Gemayel and his bodyguard.
Lack of knowledge is dangerous because it leaves people to draw conclusions based on their prejudices.
And in Lebanon, already divided, that usually means the hardening of opposing views, which divide this nation even more seriously and deepens its sectarian fault lines.
Big political funerals like that of Pierre Gemayel can release tension sometimes, but his did not.
The crisis that had gripped Lebanon since the summer continues, is now worse and, if it is not resolved, this country - prodded by the powerful foreigners who support the government and its opposition - will lurch into the next phase of its sad story.