The assassination on Friday of General Wissam Al Hassan, in the Beirut neighbourhood of Achrafiyeh, was a message sent in various directions. But above all it was a devastating blow to the former prime minister, Saad Hariri, and to the March 14 coalition that opposes Syria.
As head of the Information Department of the Internal Security Forces, Gen Al Hassan was the keeper of the secrets. Among pro-March 14 security figures he was perhaps the man with the greatest insight, along with his superior, Ashraf Rifi, into the murkier corners of Lebanese political life.
Gen Al Hassan had long been a target of the Syrians and Hizbollah, but, typical of the intelligence world, he was also in regular contact with the chief of Hizbollah's intelligence service. He had even flirted with the Syrians, when Mr Hariri negotiated an uneasy rapprochement with Damascus after the 2009 elections under Saudi pressure.
The general also played a central role in the recent arrest of a pro-Syrian Lebanese former minister, Michel Samaha, who stands accused of plotting bomb attacks in Lebanon in conjunction with Ali Mamluk, a top Syrian security official. Many observers, rightly, have interpreted Gen Al Hassan's killing as payback for Mr Samaha's apprehension, and will point to the fact that he was killed very near to Mr Samaha's apartment.
But at the same time, the killing was about more than payback. It was also a warning to Mr Hariri, who was Gen Al Hassan's political sponsor. The former prime minister left Lebanon in April 2011, in part because he feared assassination. Gen Al Hassan's fate will guarantee Mr Hariri stays away even longer, leaving a void in Sunni political ranks.
Mr Hariri has also assisted Syrian rebels, and it is probable that Gen Al Hassan supported this agenda. His elimination will hinder the efforts of the Lebanese foes of Syrian President Bashar Al Assad to gain the initiative at home against the Syrian regime's partners.
Gen Al Hassan, a Sunni from northern Lebanon, was someone with a close eye on Islamist movements in his area of origin. He had infiltrated many Islamist groups in Tripoli, and his death means that the Internal Security Forces will need some time to rebuild their knowledge base in the city. At a moment when the northern Islamists are mobilising in favour of the Syrian uprising, this is worrisome, as it means the state has less ability to establish what is going on in those circles. General Rifi is also from the north, so he can partly compensate for this intelligence void. But he is scheduled to retire at the end of this year.
The killing of Gen Al Hassan was also a broader message to the members of Lebanon's political class, above all President Michel Suleiman, that there will be retribution for distancing themselves from Damascus. In the aftermath of the Samaha affair, Mr Suleiman, like Prime Minister Najib Mikati, became more outspoken about Syria's destabilisation of Lebanon. Now they can measure the consequences: Lebanese concord can be undermined at any moment, leading to a ruinous confrontation between Sunnis and Shiites.
The question is who was behind the bombing that killed Gen Al Hassan and injured about 80. The prevailing view in Beirut is that Syria ordered the operation, but that it was implemented by Hizbollah, which alone has the network to know Gen Al Hassan's movements and act on this in real time. Samir Geagea, the head of the Lebanese Forces party, accused Syria and its Lebanese allies, by which he implicitly meant Hizbollah. The Druze leader Walid Jumblatt blamed Mr Al Assad but not Hizbollah explicitly, mainly to avoid falling into a Syrian trap of heightening sectarian hostility.
There had been speculation that Syria took the odd step of enlisting the militarily untested Mr Samaha in a bombing campaign with the aim of provoking sectarian clashes because Hizbollah was reluctant to do so on Syria's behalf. The rationale was that the party, though close to the Assad regime, had no desire to exacerbate Sunni-Shiite animosities, as this might suck it into a debilitating civil conflict.
If true, then how does one explain the assassination of Gen Al Hassan? It's possible that Hizbollah, if it was indeed involved in the crime, had little latitude to refuse a Syrian request to get rid of the general. More likely, it saw an advantage in removing a man who was regarded as a favourite to succeed Gen Rifi, and concluded that sectarian tensions could be contained.
Above all, there was benefit in removing a Sunni who headed an institution, and had the skills, to stand up to Hizbollah in a post-Assad period, when the party will seek to consolidate its hold on Lebanon without Syrian backing.
Gen Al Hassan was no choirboy. He visited Damascus for a meeting with Mr Al Assad in the interregnum when Mr Hariri's ties with Syria improved. To senior Lebanese politicians, such a political reward must have involved a quid pro quo. No one could deny Gen Al Hassan's litheness, a quality of good intelligence chiefs - and he certainly was one. A replacement will not be found easily.
Michael Young is opinion editor of The Daily Star newspaper in Beirut, which is majority owned by Hariri companies
On Twitter: @BeirutCalling