Donald Trump, on Wednesday, became the latest American to wonder whether when al-Qaeda attacked the United States on September 11, 2001, it could have had some help from the government of Saudi Arabia.

"It wasn't the Iraqis, you will find out who really knocked down the World Trade Center, 'cause they have papers in there that are very secret, you may find it's the Saudis, okay? But you will find out," Trump said in South Carolina.

Trump, in his colorful way, was referring to long-swirling theories of possible Saudi support for the attackers, and to a still-secret congressional report that investigated these very questions.

Unsurprisingly, Trump was straying into conspiracy. But his allegations were not so far removed from a scenario that's been considered within the US government itself: Could rogue Saudi officials, acting without sanction from their government, have funneled state resources to aid the attackers?

This past June, the CIA's Office of the Inspector General finally released the findings of its internal investigation, concluded in 2005, into intelligence failures leading up to the attacks of September 11, 2001. The few sections left unredacted in the 500-page report did not appear to offer any major revelations. (Note: this article first published in June when the CIA report was released; it has been updated to reflect Trump's comments.)

But the very final section of the report, titled "Issues related to Saudi Arabia," touches on a question that has swirled around US inquiries into 9/11 since the first weeks after the attacks: Was there any involvement by the government of Saudi Arabia?

This section of the report is entirely redacted, save for three brief paragraphs, which say the investigation was inconclusive but found "no evidence that the Saudi government knowingly and willingly supported the al-Qaeda terrorists." However, it adds, some members of the CIA's Near East and Counterterrorism divisions speculated that rogue Saudi officials may have aided al-Qaeda's actions.

Saudi Arabia's shortsighted support for extremism has been blowing up in its face since the 1920s

The findings, though frustratingly inconclusive, are in line with what many analysts and journalists have long suspected: that while the Saudi government was probably not involved, rogue Saudi officials sympathetic to al-Qaeda may have been.

Like so many investigations into Saudi links to 9/11, this report adds credence to the "rogue officials" theory, but it ultimately settles nothing.

What do we actually know about Saudi Arabia's possible links, or lack thereof, to Osama bin Laden and the attacks of 9/11? Why has this question so persisted in the years since the attacks? Why has it never been settled?

To understand those questions, you have to understand Saudi Arabia's complex double game with al-Qaeda and violent jihadists, the shadowy Saudi government agency that may have been the most likely base of such rogue officials, and the story of a still-secret congressional report on this very question.

The infamous and still-secret 28 pages on Saudi Arabia and 9/11

When people in the US talk about the still-lingering questions over Saudi involvement in 9/11, they will often mention that still-secret congressional report, which has achieved such infamy that it is sometimes described only as "the 28 pages."

In 2002, shortly after a Joint Congressional Inquiry into the 9/11 attacks concluded its report, the Bush administration, which has longstanding ties to the Saudi royal family, ordered that the inquiry permanently seal a 28-page section that investigated possible Saudi links to the attack.

Some members of Congress who have read the report, but are barred from revealing its contents, describe it as damning. An unnamed member of Congress told the New Yorker, "The real question is whether it was sanctioned at the royal-family level or beneath that, and whether these leads were followed through."

Other officials, though, say the findings are speculative and inconclusive, and that their release would cause unwarranted damage to the US-Saudi alliance, which has grown increasingly fragile in recent years.

The kingdom has played a double game with extremists for decades

After the Joint Congressional Inquiry, the 9/11 Commission formed to independently investigate the attacks. Their investigators followed up the same details and questions on possible Saudi involvement, and even hired some of the same staffers who had worked on the Joint Congressional Inquiry. But the 9/11 Commission ultimately dismissed the Joint Congressional Inquiry's findings on Saudi Arabia as unsubstantiated.

Because the 28 pages are still sealed and cannot be independently examined, but have been the subject of so much debate and speculation, they have become something of a Rorschach test for how one considers the question of possible Saudi involvement in 9/11. It can be helpful, then, to step back and look at what we know for sure about the country's history with Osama bin Laden, al-Qaeda, and jihadists. And we know a great deal.

Saudi Arabia's tangled history with Osama bin Laden and jihadists

Osama bin Laden, who, like many Saudis of his generation, grew up disillusioned and confused by the collision of old and new in his rapidly changing country, used his vast inheritance to fight the Soviet invasion of Afghanistan in the 1980s. There he met other Arab fighters, self-described jihadists with whom he formed al-Qaeda in 1988. The Saudi government, which along with the US backed the Afghan jihad as official policy, supported bin Laden. He came home in 1990 a national hero.

Saudi Arabia began its breakup with the jihadists, including bin Laden, that same year. Bin Laden personally met with Prince Sultan, the national defense minister, to ask permission to lead his jihadist fighters against Saddam Hussein's armies in neighboring Kuwait. When Sultan refused, bin Laden turned against the monarchy, publicly condemning it and questioning its legitimacy. In 1992, Saudi Arabia revoked his citizenship and expelled him to Sudan. In 1996, under US pressure, Sudan expelled him to Afghanistan.

By 1996, bin Laden had come to blame his problems, and the problems of the Muslim world, on the United States, which he saw as a heretical imperial power little different from the Soviet Union. Salvation could only come through defeat of nonbelievers, which to him included the American-allied Saudi royals, and the establishment of a vast pan-Islamic empire.

Bin Laden, once a Saudi hero, became a public enemy

Saudi Arabia was well aware of the threat posed by bin Laden and the movement he represented. As always, though, the Saudis played a double game: Saudi Arabia disavowed bin Laden but was one of only three countries, along with Pakistan and the United Arab Emirates, to officially recognize the Taliban, an extremist group that had seized Afghanistan by force and officially sheltered bin Laden and al-Qaeda.

This spoke to the contradictory nature of Saudi policy, that pre-2001 it opposed al-Qaeda but supported the Taliban, though the two were nominally allies. (Saudi Arabia dropped its support for the Taliban after 2001.) Such contradictions have, understandably, fed suspicions about Saudi Arabia's real agenda with al-Qaeda.

But this double game was in line with decades of Saudi government policy, which saw religious extremists as a terrible threat to the kingdom, but that sought to fight the extremists at some turns but to co-opt or appease them at others.

These tactics had another appeal: They sometimes furthered Saudi foreign policy interests. Supporting Saudi fighters in 1980s Afghanistan had been a way to funnel them away from home, where they could cause trouble. (A group of extremists had killed dozens in the traumatic 1979 siege of Mecca's Grand Mosque.) But this policy also gave Saudi Arabia influence on the Afghan battlefield and a way to undermine the Soviet Union, which it hated and feared.

It was a dangerous game, and only a matter of time until it led to catastrophe.

The problem with theories that Saudi Arabia backed 9/11

Saudi Arabia's record of backing jihadists and of a shadowy, playing-both-sides strategy has raised understandable suspicions about the country's possible links to 9/11.

But theories of the Saudi government deliberately sponsoring the attacks miss two crucial facts. First, while the Saudis had in the past supported bin Laden, by 2001 they had utterly turned against one another, with bin Laden openly seeking the royal family's destruction.

Second, while the Saudi policy of supporting jihadists was and remains disastrously shortsighted, that shortsightedness is part of what makes conspiracy theories of an elaborate Saudi-9/11 plot so far fetched. The Saudis would never support an attack on their ally and patron, and theories to the contrary make as much sense as accusing Israel or George W. Bush of responsibility.

However, there are grounds to suspect that rogue elements within the Saudi government could have plausibly aided the 9/11 attacks, and could have even done so using Saudi government money, operating out of a Saudi government agency. That agency is the Ministry of Islamic Affairs.

Could rogue Saudi officials have been involved?

In 1991, Iraqi leader Saddam Hussein invaded Kuwait; Saudi Arabia, fearing it could be next, invited the US military to station thousands of troops in the kingdom. The country's powerful and ultraconservative clerical establishment was outraged, seeing this as a humiliation and a desecration of Muslim holy land, and openly hinted they might support a coup or violent uprising. Meanwhile, many Saudi jihadists, such as bin Laden, had returned home from Afghanistan, giving the threats real teeth.

The Saudi royal family responded to this crisis as they had many times before in the country's history: by co-opting and appeasing the clerical establishment. They did this in part by shutting down some nascent liberalizing reforms that had angered ultraconservative clerics. They also established the Ministry of Islamic Affairs, a government agency that ostensibly supported Islamic charities but also funded Islamist extremism and jihadism throughout the Muslim world.

The plan worked; the Saudi clerical establishment directed their energies toward causing trouble abroad, which the Saudis tolerated. At the same time, the Saudis also cracked down on extremists who would not get in line, including bin Laden. But like so many Saudi policies to simultaneously counter and appease extremists, it was shortsighted and dangerous. The Ministry of Islamic Affairs, closely tied to the Saudi clerical establishment that had never really been under the government's control, operated with an unusual degree of autonomy.

No real evidence has emerged suggesting an official Saudi policy of backing the 9/11 attacks. However, a handful of inconclusive but highly disturbing details have come out that suggest possible links to the Ministry of Islamic Affairs.

For example, a Saudi living in the US who had ties to the Islamic Affairs Ministry, and who was salaried by a Saudi aviation company for whom he never actually did any work, facilitated and paid for an apartment for two of the 9/11 hijackers. His US-based contact in Islamic Affairs, Fahad al-Thumairy, was expelled from the US in 2002 over suspected ties to terrorists.

Such details, along with the Ministry of Islamic Affairs' unusual autonomy and its links to an ultraconservative clerical establishment that could be at times more sympathetic to jihadists than to their own government, have long fed speculation that rogue officials in the ministry could have played a role. That may be the very speculation we're seeing in the just-released CIA report.

It would be within the realm of possibility — and, indeed, would be consistent with the history of self-defeating Saudi policies — if Saudi Arabia's shortsighted support for jihadism had unintentionally allowed extremists within Islamic Affairs to divert funds to the hijackers.

Saudi Arabia's support for extremism has been blowing up in its face since the 1920s; it was perhaps only a matter of time until it blew up in our face as well.