The 2005 assassination caused outrage in Lebanon
An international court set up to try the suspected killers of former Lebanese Prime Minister Rafik Hariri has opened in the Netherlands.
The tribunal, sitting at the Hague, is expected to ask Lebanon to hand over four pro-Syrian generals held over the February 2005 killing within weeks.
Mr Hariri and 22 other people died when a massive blast ripped through Mr Hariri's convoy in Beirut.
His allies have accused Syria of involvement, a charge Damascus denies.
A trial date has yet to be set and court officials have said proceedings could last for five years.
Rafik Hariri's son, Saad, told the BBC he welcomed the start of the tribunal.
"We've been waiting for this tribunal for quite a long time, and finally we see at least a glimpse of light that impunity in Lebanon will find its way, and all these killings will end."
The Canadian prosecutor, Daniel Bellemare, has 60 days to ask the Lebanese authorities for suspects to be transferred to the Special Tribunal for Lebanon.
Mr Bellemare said he would make the call "as soon as possible".
"I will submit an indictment when I am satisfied personally and professionally that I have enough evidence," he said at the ceremonial opening of the tribunal.
The four men in custody were pro-Syrian generals who all held senior positions in the country's security infrastructure.
They are former head of General Security Maj Gen Jamil al-Sayyad, former chief of police Maj Gen Ali Hajj, former military intelligence chief Brig Gen Raymond Azar and Republican Guard commander Mustafa Hamdan.
Last week, three civilians, two of them Lebanese and one Syrian, were released from custody.
The court, with 11 judges, was created in 2007 by the UN, but opened with a formal ceremony on Sunday.
The tribunal is what many Lebanese have long been waiting for, says BBC correspondent Natalia Antelava in Beirut.
The assassination caused such a public outcry in Lebanon that Syria was forced to withdraw its troops, ending its 30-year domination of Lebanon, and changing the course of the country's history, she added.
The allies of the former prime minister blamed it on Syria, which was then Lebanon's political master.
Damascus has always denied it had anything to do with the attack, but in its early stages the UN investigation implicated top-level Syrian security officials, including the president's brother-in-law.
However, the current investigator has been much less outspoken and it is not clear whether the tribunal will have enough evidence to prove a link to Syria.
And some in Lebanon are sceptical about whether the tribunal will ever be able to uncover the full truth - especially because the overall political climate in the region has changed, our correspondent adds.
Syria and Lebanon have recently established diplomatic ties and the West is keen to improve its relations with Damascus.
The UN's under-secretary general for legal affairs, Patricia O'Brien said it was vital that the tribunal's investigation was transparent.
"A key element for the success of the Special Tribunal is not only that justice be done but that also justice must be seen to be done.
"As the Special Tribunal seat is located outside Lebanon, the development of an effective and comprehensive outreach programme bringing the activities of the Special Tribunal closer to the population of Lebanon and the wider region is a priority."