Special counsel Robert Mueller and his team of lawyers won their first conviction, sending Alex van der Zwaan to jail on Tuesday. They are methodically working their way through their investigation into Russian meddling in the 2016 election, with 19 indictments and five pleas thus far.

Everyone wants to know whom the investigation will target next. But the people who actually know, Mueller and his team of at least 17 people, have done something remarkable for Washington in the Trump era — prevented almost anything of real substance from leaking.

Mueller and his team have reached surprise plea deals with several campaign aides increasingly close to President Donald Trump, including George Papadopoulos, Michael Flynn, and Rick Gates, with reporters in the dark until just before their court appearances.

That’s probably because Mueller is a man uniquely qualified to keep secrets, with a history of minimizing his own interactions with the press. He’s also someone who has spent part of his post-FBI career literally trying to find leakers. In 2014, the NFL hired Mueller, then in private practice, to investigate its handling of a domestic abuse case involving running back Ray Rice. Mueller devoted about half of his investigative findings in his 92-page final report to his efforts to find an anonymous NFL employee who made a phone call to a law enforcement official, a story that was leaked to the Associated Press.

“Bob Mueller runs a very tight ship, and that ship does not leak,” David Kris, a former assistant attorney general for national security who worked closely with Mueller for years, told me. “He’d rather do his talking through his work.”

It starts with the fact that Mueller doesn’t like talking to reporters. He’s been in high-profile positions for decades, culminating in a 12-year stint as FBI director. And during that time, he did not warm to the press, according to Peter Zeidenberg, a former federal prosecutor who worked with Mueller at the Justice Department.

“He’s a serious guy, and he hates people who talk to the press,” Zeidenberg said. “It’s anathema to him.”

Even so, Mueller’s success at preventing leaks — especially given the huge number of reporters working as hard as possible to break news about his probe — stands out in Trump’s Washington, where White House aides routinely share embarrassing and private information with the press. When then-White House press secretary Sean Spicer held a meeting with staff to try to crack down on leaks in February 2017, for example, details of the meeting immediately leaked.

Mueller also benefits from having a small team primarily made up of lawyers he’s worked with for years. They know that leaks could fuel the conservative attacks on Mueller, whom Trump accuses of running a politically motivated “WITCH HUNT,” or even cost them their jobs.

“The last thing that any of those people would want to do is let Mueller down,” Zeidenberg said.

Mueller has kept his team together, which helps prevent leaks

The nearest comparison to Mueller’s investigation is Ken Starr’s four-year probe of President Bill Clinton. That investigation, spanning Clinton’s two terms, was marked by a huge amount of staff turnover. And every time somebody left, it was another chance for reporters to get a bit of insight into what was happening inside Starr’s team.

That included Charles Bakaly III, who was accused of leaking information on the investigation and was fired by Starr. A judge later acquitted Bakaly of criminal charges.

“Ken Starr’s record for leaking was notorious,” Lanny Davis, who served as special counsel to Clinton, told me.

Mueller’s team, by contrast, has stayed largely intact from the beginning. Only one lawyer has left Mueller’s team thus far, although his departure was highly controversial. Peter Strzok, a counterintelligence specialist on Mueller’s team, shared a string of text messages with FBI lawyer Lisa Page describing their mutual dislike of Trump. Strzok and Page were engaged in an extramarital affair at the time.

Mueller stepped in and removed Strzok in the summer of 2017 when he found out about the text messages, but that hasn’t stopped conservatives from claiming that the messages proved Mueller’s team is biased against Trump.

“This goes to intent to action,” Rep. Jim Jordan (R-OH), a prominent anti-Mueller Congress member, told reporters in December about the text messages. “That to me is big.”

But other than Strzok, Mueller’s team remains intact. The majority of the team comes from within the Justice Department, although Mueller added several outside lawyers who have worked with him for years.

Aaron Zebley, who served as Mueller’s chief of staff while he was at the FBI and followed him to the WilmerHale law firm after Mueller left government in 2013, joined the special counsel’s office to manage the investigation.

James Quarles, who worked on the Watergate investigation that ended Richard Nixon’s presidency, also came over from WilmerHale and is now the primary liaison between the investigation and the White House.

Even most of the Justice Department lawyers on the team worked with Mueller for years while he was with the FBI.

The team’s rapid pace and long history with Mueller are likely preventing leaks, Kris, who worked directly with the former FBI chief at the Justice Department, told me.

“Mueller inspires loyalty,” said Kris, who now runs the Culper Partners consulting firm. “His achievements here probably inspire loyalty.”

Some of the staff from WilmerHale also worked with Mueller on his last high-profile investigation, an inquiry into how the NFL handled reports of spousal abuse by Ray Rice, who was a Baltimore Ravens running back. And much of that probe would focus on trying to find an NFL employee who had reportedly leaked information claiming the NFL had known of the abuse months earlier than the league had admitted.

Mueller has gone hunting for leaks before

In 2014, the NFL was dealing with the fallout of shocking footage showing Ray Rice assaulting his fiancée in February of that year. The footage showed Rice punching Janay Palmer in an elevator, appearing to leave her unconscious. League officials claimed not to have seen the video before.

The NFL had suspended Rice for two games in July of 2014 after word of the incident broke, but it wasn’t until media outlets started playing the video that the league suspended Rice indefinitely. He eventually got the ban overturned in court, but he hasn’t played since.

The controversy centered on whether the league had let Rice off too easy with its initial suspension, but when league officials approached Mueller, they wanted him to focus on a much smaller detail — what the league knew about the incident before news outlets got the video.

An AP report said an NFL employee had called from league headquarters and left a voicemail for a law enforcement source confirming receipt of the video on April 9, 2014, months before the video was made public. One of Mueller’s primary jobs was to find this person at NFL headquarters, as the call undermined the NFL’s defense that it didn’t know about the video.

Mueller and his team, which included Zebley, aggressively pursued the unnamed female NFL employee mentioned in the AP report.

“We also interviewed every female employee, contractor, vendor, or intern whose electronic badge recorded that she was in the League’s main office on April 9, the date the alleged call was made,” Mueller wrote in his final report.

In all, Mueller’s team interviewed 188 women who denied making the call, according to Mueller’s report, which he delivered to the NFL in January 2015. Mueller’s team also pored over records of 1,583 calls to 1,050 telephone numbers made on April 9 from the league office, and searched all the NFL’s computers for evidence the league had the video, using a range of forensic tools.

Mueller faced criticism for the narrow scope of his investigation, but he completed the job in only four months, and the NFL applauded his work.

Mueller could use the recent experience with digital tools to hunt for leaks from his special counsel team, but experts say technical tools don’t solve leaks.

Mueller could spy on his team, but it wouldn’t help

Mueller has forensic tools now that he could use to keep an eye on who his team is talking to, and most investigations, including his probe into Russia, place strict rules on the handling of information.

“The Special Counsel’s Office has undertaken stringent controls to prohibit unauthorized disclosures that deal severely with any member who engages in this conduct,” Peter Carr, the Russia investigations spokesperson, told me via email. He declined to elaborate on what those controls are.

But those who have worked with Mueller said that forensic tools won’t keep information from leaking.

“If people want to leak information, and think that’s okay, it’s very difficult to set technical measures to prevent them from doing so,” Kris told me.

Mueller also hasn’t decided to actively leak information.

Lawyers I spoke to described leaking as a slippery slope. Once you start, it’s hard to stop, and you lose the moral high ground. You also lose the element of surprise.

“The fact that they’re not leaking, and that nobody they’re talking to knows where the investigation is going and what their targets are, it makes it really difficult for the defense,” Zeidenberg told me.

The leaks help a legal defense figure out how to combat charges and questions from investigators. Without the leaks, defense lawyers only know about what their clients are directly asked, or what court documents say.

If Mueller gets removed, it could change the equation. His team might want to get information out to make sure it’s not buried. That’s what happened when Nixon fired Archibald Cox, the special prosecutor investigating the Watergate scandal. His team began to leak information on what they’d found to help defend Cox.

But to date, very little information has spilled out from the Mueller team, although that might be a reflection of Mueller’s personality. When a federal judge picked Mueller to mediate a settlement in 2016, he had a simple description of Mueller: “a person who can actually keep a secret.”