President Donald Trump had almost certainly never heard the name Aaron Zebley before the announcement that the former FBI agent was joining the special counsel investigation into ties between Trump’s campaign and Russia. But to those who have followed the arc of the bureau during the past twenty years, Zebley’s is a name that underscores just how far-reaching and dogged—and potentially long—the probe will likely be.

Just ask Steve Gaudin’s ex-girlfriend.

She wasn’t at all happy when Zebley, her boyfriend’s FBI partner, called at 3 one morning in August, 1999. Despite all of Gaudin’s international travel, chasing al Qaeda long before the terrorist group was a household name, he and his girlfriend had managed to settle down in New York City and carve out a life together in between his overseas terrorist hunts. The couple was even looking forward to an imminent, albeit brief, summer vacation.

But then came the call from Zebley.

“I’ve found Ali Mandela,” Zebley said, excitedly. Mandela, the fugitive terrorist suspected of helping execute the previous year’s bombings of US embassies in East Africa, appeared to still be on the continent, he told Gaudin. Somewhere in South Africa. They had to leave immediately.

Angry at yet another sleepless night—and vacation—ruined by the bureau’s demands, Gaudin’s girlfriend gave him some advice: Don’t bother coming back.

But that was just the way it was for the elite agents on one of the FBI’s most storied squads. Nothing could come between them and their search for justice.

The details of that trip—and the subsequent capture of one of America’s most wanted terrorists by Zebley and Gaudin—help illuminate the makeup of the special counsel team that former FBI director Robert Mueller is assembling. It’s a team that contains some of the nation’s top investigators and leading experts on seemingly every aspect of the potential investigation—from specific crimes like money laundering and campaign finance violations to understanding how to navigate both sprawling globe-spanning cases and the complex local dynamics of Washington power politics.

Meet Mueller's Roster

As Mueller begins investigating Russia’s interference in last year’s election and its possible links to Donald Trump’s campaign, he is quietly recruiting lawyers and staff to the team. And in recent days, Trump associates have stepped up criticism of Mueller and his team—including a report, quickly rejected by the White House, that Trump is considering firing Mueller before he even gets started.

Tuesday morning on Good Morning America, Newt Gingrich blasted Mueller and his still-forming team. “These are bad people,” Newt Gingrich told George Stephanopoulos. “I’m very dubious of the team.”

But that criticism flies in the face of widespread, bipartisan acclaim for the team. In fact, just a day earlier, on the same program, former Whitewater prosecutor Ken Starr praised Mueller at length. “I don’t think there’s a legitimate concern about Bob Mueller,” Starr said, explaining that the former FBI director was “honest as the day is long.”

From the list of hires, it’s clear, in fact, that Mueller is recruiting perhaps the most high-powered and experienced team of investigators ever assembled by the Justice Department. His team began with three lawyers who also quickly left WilmerHale, the law firm where Mueller has also worked since he left the FBI in 2013—Zebley, James Quarles III, and Jeannie Rhee.

The rapid recruitment of Quarles attracted immediate attention: A famed litigator who was an assistant special prosecutor for the Watergate investigation, Quarles specialized in campaign finance research for the Watergate task force, which surely will be an area of focus for Mueller’s investigation. (The FBI has been serving subpoenas regarding the finances of campaign adviser Michael Flynn and campaign chairman Paul Manafort, both of whom have retroactively registered as foreign agents, admitting that they were paid by foreign governments during the period when they were also advising Trump.) In more recent years, Quarles has risen through the law firm’s ranks to run its DC office, and is an experienced manager. In granting him the firm’s top recognition in 2007, one of his colleagues said that Quarles “represents precisely the values that should define us culturally and reputationally: He is an excellent lawyer, he is an extraordinary hard worker, he is the ultimate team player, and he treats everyone with respect and collegiality.”

It’s a team that’s not just a paper office tiger but one with deep experience investigating crime around the world.

More recently, Mueller has recruited Andrew Weissmann, his one-time general counsel at the FBI and a long-time adviser who once led the Justice Department’s fraud unit. In the early 2000s, Weissmann also oversaw the Enron Task Force, the storied Justice Department unit that investigated the complex machinations of the failed energy giant. (The task force’s team of prosecutors was so well-respected that they went on to dominate the Justice Department’s top ranks for the better part of a decade, including former officials like White House homeland security adviser Lisa Monaco, White House counsel Kathy Ruemmler, assistant attorney general Leslie Caldwell, and acting assistant attorney general Matthew Friedrich.)