There are two competing theories in Beirut for who killed Pierre Gemayel. They reflect Lebanon’s deep cleavage since Syrian forces withdrew amid popular demonstrations after the assassination of Rafik Hariri in February 2005.

The US-backed government and its supporters accuse Syria and, in some cases, its ally Hizbullah. They say Syria wants to scupper an international tribunal to try those accused of killing Mr Hariri. A UN report links Lebanese and Syrian security services to the Lebanese prime minister’s death, but Damascus denies involvement.

“Bottom line, there is one less minister in a government Syria and its allies want to bring down,” said Michael Young, editor of the Lebanese Daily Star of Mr Gemayel’s killing.

The theory suggests that, after six cabinet ministers resigned this month and the killing, Syria’s agents in Lebanon need kill only two more and they will achieve a collapse of the government, because it will be constitutionally inquorate. A fresh government will block the tribunal, and Damascus will avoid the embarrassment of standing trial over Mr Hariri.

Other related theories suggest rogue elements in Syrian security acting outside President Bashar al-Assad’s knowledge, seeking to intimidate Lebanese MPs in the run-up to ratification of the UN tribunal.

The other main theory accuses the US or its allies in Lebanon of killing Mr Gemayel to stop the opposition, led by Hizbullah, from bringing down the government and curtailing American influence. It also suggests an attempt to isolate Syria once again, just as the west wants to re-engage Damascus over possible help in Iraq. “The killing of Gemayel gave the embattled government a bit of breathing space and reinvigorated the pro-government forces’ withering anti-Syrian cause, which has been primarily fuelled by the assassination of its leaders,” said Amal Saad Ghorayeb of Beirut’s Carnegie Middle East Centre.

Proponents of this theory believe the killing only makes it harder for Lebanese opponents of the tribunal in its current form to vote against, for fear of being associated with a pro-Syrian agenda. “If anything this assassination has expedited the decision in the UN to pass the resolution,” said Ms Ghorayeb, referring to security council members Russia and Qatar, who had reservations, but came on board hours after Mr Gemayel’s killing.