FBI Director Louis Freeh, retiring at the end of June, calls it his "only unfinished piece of business."
The "business" is going after the Iranian-sponsored terrorists behind the bombing of the Khobar Towers in Saudi Arabia five years ago, with a toll of 19 Americans killed and 500 injured.
The mystery is why the conspiracy has remained a mystery for so long. As early as August 1996, Secretary of Defense William Perry told NPR's Martha Raddatz that Saudi Arabia would soon be announcing the results of its investigation with an international connection that he indicated would be to Iran.
The Saudi report has not been published, and the FBI was long stymied by the Saudis in its own investigation. We know a lot more of the inside story, thanks to a comprehensive article by Elsa Walsh in The New Yorker.
The Saudis' foot-dragging was not hard to figure out: fear of its pro-Iranian Shiites, fear of Iran, and fear of American retaliation against Iran. The evidence led to the high command of the Iranian Revolutionary Guard. Saudi Ambassador Prince Bandar told Mr. Freeh he feared that if the US took military action against Iran, Iran would retaliate against Saudi Arabia.
Harder for Freeh to understand was the foot-dragging in the American government. Starting with the election of moderate Mohammad Khatami as Iranian president in 1997, President Clinton began pursuing a policy of reconciliation with Iran. Freeh began having trouble with the State Department getting approval for his officers to travel to Saudi Arabia.
Mr. Clinton promised Saudi Crown Prince Abdullah not to take military action against Iran without consulting the Saudis. In November 1998, Freeh had hard evidence that Brig. Gen. Ahmad Sharifi of the Iranian Revolutionary Guard had selected the Khobar Towers as a target at the behest of Ayatollah Khameini, Iran's spiritual leader.
When Freeh went to National Security Adviser Sandy Berger to ask for indictments, Mr. Berger said, according to the FBI director, "That's just hearsay."
By the summer of 1999, Clinton was convinced there was solid evidence of Iranian involvement, and he wrote to President Khatami asking for help in the investigation. Khatami said he didn't know what Clinton was talking about.
Freeh decided to wait for a change in administrations, and now he is awaiting a decision from President Bush. He has heard that the administration will probably not oppose indictments.
If the case finally comes to prosecution, it will be almost entirely because of the doggedness of Louis Freeh.
If it doesn't, he plans at least to tell the families of the 19 Americans who did it - and, maybe, who obstructed justice.
Daniel Schorr is a senior news analyst for National Public Radio. His memoir, 'Staying Tuned: A Life in Journalism' (Pocket), has just been published.
(c) Copyright 2001. The Christian Science Monitor