Twenty years ago today, al Qaeda carried out its most devastating terrorist attack prior to the September 11 hijackings. On the morning of August 7, 1998, two al Qaeda operatives drove explosive-laden trucks into the U.S. embassies in Kenya and Tanzania. Two-hundred and twenty-four people were killed and thousands more wounded. Here is a fact about the bombings that is well-established by official sources and worth remembering: Iran showed al Qaeda how to conduct the attacks.

The Iranian hand was first detected by federal prosecutors during the Clinton administration. The relationship between al Qaeda and Iran initially developed during bin Laden’s sojourn in the Sudan in the early 1990s. At the time, bin Laden was attempting to build an “Islamic Army” comprised of various Sunni jihadist groups from around the world. The al Qaeda founder’s big tent jihadism also included outreach to Iran and its chief terrorist proxy, Hezbollah.

In early November 1998, the U.S. government indicted various al Qaeda members for the embassy bombings. The indictment included this sentence:

Al Qaeda also forged alliances with the National Islamic Front in the Sudan and with the government of Iran and its associated terrorist group Hezbollah for the purpose of working together against their perceived common enemies in the West, particularly the United States.

This allegation did not go away. Instead, official sources continued to build upon it in the years that followed. During the trial of some of those responsible for the embassy bombings, two key al Qaeda witnesses explained the collusion.

One of those witnesses, Jamal al-Fadl, had defected from al Qaeda’s ranks. Al-Fadl told a New York court that some of his comrades had traveled to Lebanon, where they received Hezbollah’s explosives training. An al Qaeda operative returned with a videotape from the training. “I saw one of the tapes, and he tell me they train about how to explosives [sic] big buildings,” al-Fadl said .

Big buildings like the American embassies in Kenya and Tanzania.

Another terrorist, Ali Mohamed, agreed to a plea deal as part of the embassy bombing proceedings. Mohamed was originally a member of the Egyptian Islamic Jihad (EIJ), a terrorist organization headed by Ayman al Zawahiri. The EIJ would later formally merge with bin Laden’s enterprise. But Zawahiri and bin Laden were already working together closely by the early 1990s. Indeed, Mohamed admitted that he had conducted surveillance on “American, British, French, and Israeli targets in Nairobi” on behalf of bin Laden. One of the targets was the same American embassy bombed in 1998.

“I later went to Khartoum, where my surveillance files and photographs were reviewed by Osama bin Laden, Abu Hafs, Abu Ubaidah, and others,” Mohamed explained. “Bin Laden looked at the picture of the American Embassy and pointed to where a truck could go as a suicide bomber.” (Abu Hafs and Abu Ubaidah were two other early al Qaeda leaders.)

Mohamed admitted that he conducted several other missions on behalf of bin Laden as well. But that was not all. Here is a transcript (slightly edited for spelling) of what Mohamed said about al Qaeda’s relations with Iran and Hezbollah:

I was aware of certain contacts between al Qaeda and al Jihad organization [EIJ], on one side, and Iran and Hezbollah on the other side. I arranged security for a meeting in the Sudan between Mughniyah, Hezbollah’s chief, and Bin Laden. Hezbollah provided explosives training for al Qaeda and al Jihad. Iran supplied Egyptian Jihad with weapons. Iran also used Hezbollah to supply explosives that were disguised to look like rocks.

Imad Mughniyah was Hezbollah’s master terrorist. He was eventually killed in a bombing in Damascus in 2008. (The targeted bombing was reportedly a joint operation conducted by the Israelis and the United States.) Mughniyah was responsible for a string of attacks against American and Israeli targets. In 1983, under Mughniyah’s direction, Hezbollah terrorists bombed the U.S. embassy in Beirut, a barracks for the U.S. Marines and the headquarters for French service members. The latter two targets—the Marine barracks and the French facility—were struck in simultaneous suicide bombings.

The same modus operandi was employed in al Qaeda’s August 7, 1998 embassy bombings. According to Ali Mohamed, bin Laden saw how America cut and ran from Lebanon following Hezbollah’s earliest attacks. The al Qaeda founder wanted to reenact these events, this time by forcing the United States to retreat from the broader Middle East. “Based on the Marine explosion in Beirut in 1984 [sic: 1983] and the American pull-out from Beirut, they will be the same method, to force the United States to pull out from Saudi Arabia,” Mohamed explained when asked about the intent behind al Qaeda’s attacks on U.S. interests.

In 2004, the 9/11 Commission echoed Mohamed’s assessment, explaining that Iran’s and Hezbollah’s assistance provided al Qaeda with the “tactical expertise” required to carry out the embassy bombings.

It is worth quoting from the 9/11 Commission’s report at length. On page 61 we read:

In late 1991 or 1992, discussions in Sudan between al Qaeda and Iranian operatives led to an informal agreement to cooperate in providing support—even if only training—for actions carried out primarily against Israel and the United States. Not long afterward, senior al Qaeda operatives and trainers traveled to Iran to receive training in explosives. In the fall of 1993, another such delegation went to the Bekaa Valley in Lebanon for further training in explosives as well as in intelligence and security. Bin Ladin reportedly showed particular interest in learning how to use truck bombs such as the one that killed 241 U.S. Marines in Lebanon in 1983. The relationship between al Qaeda and Iran demonstrated that Sunni-Shia divisions did not necessarily pose an insurmountable barrier to cooperation in terrorist operations. [emphasis added]

There are additional details on page 68, three paragraphs into the 9/11 Commission’s section on the embassy bombings. We learn that after personally reviewing the surveillance reports in 1994, bin Laden and his lieutenants agreed that the “U.S. embassy in Nairobi was an easy target because a car bomb could be parked close by.” They “began to form a plan,” which was made easier by Iran’s and Hezbollah’s assistance. On page 68 we read:

Al Qaeda had begun developing the tactical expertise for such attacks months earlier, when some of its operatives—top military committee members and several operatives who were involved with the Kenya cell among them—were sent to Hezbollah training camps in Lebanon.

(A U.S. district court later agreed with this assessment, issuing a default judgment against Iran for its role in showing al Qaeda how to carry out the bombings.)

The 9/11 Commission’s footnotes point to al-Fadl’s and Mohamed’s testimony, but they also cite additional intelligence reporting. One such report, dated January 31, 1997, was titled, “Establishment of a Tripartite Agreement among Usama Bin Ladin, Iran, and the NIF.” (The NIF was Sudan’s National Islamic Front.) Another intelligence report, dated they same day, was titled, “Cooperation among Usama bin Laden’s Islamic Army, Iran, and the NIF.” Heavily redacted versions of these reports were subsequently made available to the public. While it is impossible to read much of the intelligence cited, it is clear that the U.S. government was aware of Iran’s relationship with al Qaeda more than a year and a half before the 1998 U.S. embassy bombings.

A declassified passage included in the January 31, 1997 reports reads: “Eventually an agreement was reached to collaborate politically and militarily. The primary goal of this collaboration was to confront Israel and the United States, while the secondary goal was to undermine Arab regimes which supported Israel and the United States.” The authors of the report added: “After the agreement was reached . . . [redacted] . . . Experience from Hizballah and Iran should be transferred to new nations/extremist groups who lack this expertise. This would then allow Islamic Army members to gain the necessary experience in terrorist operations.”

The end result of Iran’s willingness to transfer its terrorist know-how to al Qaeda’s “Islamic Army” was the U.S. embassy bombings in 1998.

Some commentators, including a former Obama administration official , impugn the motives of anyone who raises the issue of Iran’s relationship with al Qaeda. They argue that this is all about justifying a war with Iran. That is an attempt to change the conversation.

But facts are stubborn. The evidence cited above comes from Clinton-era federal prosecutors, al Qaeda witnesses, the bipartisan 9/11 Commission Report, and Clinton-era intelligence reports. To this list we may add a string of additional official pronouncements. Between July 2011 and July 2016, the Obama administration’s own Treasury and State Departments repeatedly pointed to a separate “agreement” between the Iranian regime and al Qaeda. This arrangement allows al Qaeda to operate its “ core facilitation pipeline ” on Iranian soil.

This is not all there is to Iran’s dealings with al Qaeda. There have been multiple antagonistic episodes between the two sides. From his safe house in Abbottabad, Osama bin Laden considered Iran’s increasing regional footprint to be a menace and weighed plans to counter it. Al Qaeda’s branches have also fought Iranian proxies, including Hezbollah fighters, on the ground in Syria and Yemen for years. Anti-Iranian rhetoric is a regular feature of al Qaeda’s propaganda and other statements.

Yet, some al Qaeda leaders have managed to maintain a foothold inside Iran despite of the conflict between the organization and the state. One of them is Saif al-Adel, a senior member of al Qaeda’s management team. After the 9/11 hijackings, al-Adel fled to Iran, where he likely operated for some time before being placed under some form of arrest. (Some reports implicated him in the May 2003 bombings in Riyadh.)

The details of al-Adel’s time in Iran have always been murky. Bin Laden’s files show that al-Adel was imprisoned for a time, and this became a point of contention. Eventually, in 2015, the Iranians reportedly freed him as part of a hostage exchange . More recently, in late 2017, an al Qaeda operative in Syria revealed that al-Adel was “not imprisoned” inside Iran, but instead allowed to “move around” and make decisions on behalf of the organization.

This shouldn’t be altogether surprising. Al-Adel has benefitted from Iran’s assistance. Testifying before a New York court in early 2001, Jamal al-Fadl named al-Adel as one of the al Qaeda operatives who attended Iran’s and Hezbollah’s terrorist training in the early 1990s.

Al-Adel has long been wanted by the FBI for his role in the 1998 embassy bombings. Two decades after that heinous attack, he still hasn’t been brought to justice. And during much of that time, the Iranians have known his whereabouts.

Thomas Joscelyn is a Senior Fellow at the Foundation for Defense of Democracies and the Senior Editor for FDD’s Long War Journal. Follow him on Twitter @thomasjoscelyn.

Follow the Foundation for Defense of Democracies on Twitter @FDD. FDD is a Washington-based nonpartisan research institute focusing on national security and foreign policy.