The downing of Flight 103 was an attack of major proportions: aside from the 1983 truck bombing that killed 241 Marines in their barracks in Beirut, it took more American lives than any other terrorist strike up to that point in history. The death toll from the incident remains the third highest from terrorism in the nation’s history.

It was also a sign of things to come—a shocking prelude to a new age of international crime and terror. The investigation that followed was itself a harbinger—both massively complex and multinational in scope. The case was led by Scottish constables, British authorities, and the FBI, but it also involved police organizations in Germany, Austria, and Switzerland and intelligence agencies from many of these countries. Investigators turned up tiny bomb fragments that eventually pointed to a pair of Libyan intelligence operatives, who were indicted in the U.S. and Scotland and tried in the Netherlands. The chief U.S. prosecutor was none other than Robert Mueller, the future FBI director.

The FBI had been investigating international crime and working with global partners for years—including with the Canadians beginning in the late 1920s and the British starting in the late 1930s. The Bureau had set up its first international offices, or legal attachés, in the 1940s in Mexico City, London, Ottawa, Bogotá, Paris, and Panama City, followed by Rome and Tokyo in the 1950s. But the coming international crime wave would be of an entirely different magnitude.

It would be driven by two major forces.

First, around the same time that Pan Am Flight 103 was exploding into a million pieces, a shadowy terrorist organization was secretly starting to come together in the Middle East.

With their surprising victory over Soviet forces in Afghanistan in the late 1980s, tens of thousands of foreign mujahadeen who’d joined the struggle were brimming with confidence, wanting to advance their Islamic cause in other parts of the world. One group that congealed during this time was called “al Qaeda, or “the Base.” Its leader—Usama bin Laden—was the son of a wealthy Saudi businessman and a successful merchant in his own right. After centering operations in Sudan in 1992, bin Laden began formulating plans to attack the West with an evolving, deadly new brand of jihad. The following year, Ramzi Yousef—a young extremist who’d trained in one of bin Laden’s camps—would lead the first major Middle Eastern terrorist attack on American soil by planting a truck bomb beneath the World Trade Center.

It was just the beginning. Bin Laden and his supporters would later move to Afghanistan, where an alliance with the Taliban government gave them a secluded safe haven for training recruits and planning attacks, more of which were just around the corner.

Second, the international landscape had begun changing in ways that didn’t seem possible just a few years earlier, and the resulting shifts would have a profound impact on the state of security worldwide.