On March 8, 1985, at the height of Lebanon's civil war, a team of Lebanese hard cases hired by the CIA killed 80 people in a car bombing in the Hezbollah-controlled south Beirut district of Bir el-Abed.
The bomb was intended to assassinate Sayyed Mohammed Hussein Fadlallah, then considered Hezbollah's "spiritual guide." The much-revered cleric survived, saved from walking into the blast by a girl who delayed him as he left his mosque.
But the attack triggered a blood feud between the Iranian-backed movement and the Americans that's still running.
Even so, Lebanese officials say the CIA, possibly seeking to avert a religious war that could tear Lebanon apart, tipped off its Shiite adversaries last week about a bomb plot in Bir el-Abed, this time supposedly by Sunni extremists linked to al-Qaida who have become Hezbollah's mortal enemy.
An estimated 75 pounds of high-grade explosive in a Renault Rapide van was detonated July 9 in a parking lot at mid-morning, possibly by a timer but maybe by remote control. More than 50 people were wounded.
It's not at all clear why the CIA would alert Hezbollah to a planned attack deep inside one of its most secure areas, in a district where many of the group's senior officials live and work in heavily guarded buildings that have long been targets for Israeli intelligence.
The bombing appears to be related to the bloody civil war in neighboring Syria, where Hezbollah's fighters backing the regime of President Bashar Assad against largely Sunni rebels. Hezbollah's veterans have played a high-profile role in defending a widely reviled regime and Sunni zealots have vowed revenge.
A group calling itself the 313 Brigade, supposedly linked to al-Qaida, which is fighting on the rebel side, claimed responsibility, and vowed further attacks on Hezbollah's Lebanese strongholds.
Given the murderous nature of the long war of the shadows between the CIA and Hezbollah, in which several U.S. agents have been killed, one can rule out the possibility that the CIA was concerned about civilians, undoubtedly Hezbollah supporters, being killed in the bombing.
But in the byzantine demimonde of global terrorism, it is possible the CIA was warning Hezbollah because it wants something in return, possibly against a common enemy -- like al-Qaida.
What that might be is anybody's guess. But so much blood has been spilled in this particular conflict -- think 241 Americans killed in the October 1983 bombing of the U.S. Marine barracks outside Beirut airport -- between U.S. intelligence and an organization that until Osama bin Laden happened along was considered the world's most savage and effective terrorist organization, that it must be of considerable importance to the Americans, if these reports are to be believed.
There is a school of thought in Beirut that the CIA, by alerting Hezbollah to the bombing and the possibility of other plots, wanted the Shiite organization to know the bombings were not the work of the CIA so Americans would not be targeted in retaliation.
Others believe the Americans were trying to prevent a sectarian bloodbath between Lebanon's Shiites and Sunnis, a spillover from the Syrian conflict.
The breathtaking suggestion of the CIA communicating, however obliquely, with some of its most dedicated enemies raises intriguing possibilities.
The Lebanese sources say the CIA's warning came from the agency's station chief in Beirut, who alerted Lebanese security chiefs, who passed the word to Hezbollah in its south Beirut stronghold known as the Dahiyeh.
The sources say the warning contained highly detailed intelligence the agency had apparently obtained through electronic intercepts and agents on the ground who would appear to have extraordinary access to jihadist operations.
The Al Akhbar daily, a Hezbollah mouthpiece, reported the CIA passed on such details as the names of the plot's masterminds and that a staggering 16 tons of explosives were smuggled into Lebanon for other attacks by at least three cells.
These would be aimed at Hezbollah bastions, as well as the Lebanese army, considered by many to be in Hezbollah's pocket, and the Saudi Arabian and Kuwaiti ambassadors in Beirut.
Sixteen tons suggests lots of big bombs intended to kill hundreds of people. But if these reports are correct, it's not clear why only 75 pounds were used in the Dahiyeh bombing rather than a much more destructive truck-size charge.
Watch this space.