The FBI, repository of many of the celluloid myths that shape the American mind, has betrayed an all-too-human fallibility in its efforts to track down those responsible for what appear, in the light of the evidence unfolding inch by inch in the TWA case, to have been the year's two big terrorist outrages. And, as if that were not humbling enough, the indications are that the Untouchables' case against the two men accused of last year's bombing in Oklahoma City - the worst crime ever committed on American soil - may not be as open-and-shut as it once seemed.
Each of the three incidents has received the full infotainment treatment from American TV. Each has been portrayed as an unfolding drama, replete with good guys and bad guys (with the curiosity in the Atlanta case that the security guard Richard Jewell found himself playing first one role and then the other). Each has seen the FBI presented in a heroic light, as the reassuring real-life expression of those qualities which are the ingredients of every Hollywood blockbuster and by which Americans believe they are defined: boundless optimism and faith in the belief that virtue, dedication, and hard work shall prevail.
The common goal is the happy ending, previously known as the pursuit of happiness. In the particular case of the FBI this means catching and locking up criminals. When the FBI fails to do this, and especially when it is under the national spotlight, the general happiness is diminished. TV has presented the TWA case as a whodunnit thriller. As such the cinematic expectation right from the start has been that the FBI would see justice done. Indeed, James Kallstrom, the FBI officer heading the investigation, played his tough-guy part to perfection when he promised in his first news conference that he would catch "the cowards who did this".
Things have not unfolded according to the script, however. Never mind the "cowards", the main challenge has been to establish whether the explosion was a criminal act at all. The FBI, assisted by a cast of thousands which has included the US navy and Nasa, has pursued its objective driven by another favourite American myth: that if you throw enough money and resources at a problem you will solve it. "I get anything I want," Mr Kallstrom declared at another of his news conferences. "I can use anything. I can do anything I want to do. I don't have any limitations."
The scant fruits of Mr Kallstrom's Messianic bravado were revealed in a New York Times article on Friday which said FBI scientists had found conclusive evidence of explosive particles inside the passenger cabin of the TWA flight that crashed on 17 July, killing all 230 aboard. The FBI confirmed the discovery, but crushed any premature celebrations by adding it was still too early categorically to tell whether the plane had been destroyed by a missile, a bomb or a mechanical aberration.
Either way, the FBI investigation into the plane crash has advanced significantly more slowly after five-and-a-half weeks than the investigation into the Olympics bomb had after five-and-a-half hours, by which time the precise nature of the homemade device that disrupted the revels at Atlanta's Centennial Park had already been established.
As for the identity of the culprits in each case, the FBI does not appear to have a clue. If Richard Jewell, the security guard on whom suspicion fell after the Atlanta blast, has been subjected in recent weeks to trial by TV, this has not been so much the fault of the media as of the FBI. For it was their investigators who made it known that Mr Jewell fitted the profile of the home-grown American terrorist before proceeding to ransack the apartment he shares with his mother.
Last week Mr Jewell submitted himself to a 15-hour lie-detector test, after which the former FBI agent who conducted it declared himself fully satisfied that the suspect was "totally innocent". Now Mr Jewell is demanding an apology from the FBI and hinting that he might sue for defamation.
A deeper embarrassment might lie ahead when the Oklahoma bomb trial eventually takes place. It was not so much Elliot Ness genius as freakish luck that secured the arrest of the prime suspect, Timothy McVeigh. The former soldier was caught speeding by a traffic policeman a few hours after the explosion on 19 April last year, which left 169 dead. The trail led from Mr McVeigh to his friend and co-accused, Terry Nichols, whom the FBI persuaded to implicate Mr McVeigh in the bombing. Or rather, they thought they had.
Last week a judge dealt a potentially damaging blow to the prosecution case when he ruled that statements Mr Nichols made to the FBI after his arrest may not be used in court against his co-accused. The defence lawyers, who won a significant legal battle earlier this year when the trial venue was moved from Oklahoma City to Denver, now believe they may be able to hold separate trials for the two accused. They have been encouraged, too, by a debate raging among seismologists and geophysicists as to whether it was one bomb or two that went off.
Most of the FBI evidence is under court seal, and so it is not certain how great a loss to the prosecution case the absence of Mr Nichols's testimony against Mr McVeigh will prove to be. What is known, however, is that the case is built on circumstantial evidence. No eyewitnesses have come forward to say they saw either of the two accused make, plant or detonate the 4,800lb bomb.
It may be that once again, as in the OJ Simpson trial, circumstantial evidence is not enough. But even if it is, the excruciatingly slow pace of the TWA investigation and the frustrations of the Atlanta case have yielded two pieces of evidence at least as conclusive as the chemical traces found in the wreckage of the downed Boeing 747: that in real life happiness cannot be bought, and optimism is not always rewarded.