As the FBI enters the final phases of its investigation into Hillary Clinton’s use of an unauthorized email server for government business, Attorney General Loretta Lynch and FBI Director James Comey are meeting frequently to discuss the progress and handling of the highly sensitive case, a source told Fox News.

Among the issues discussed in the meetings, which have been taking place several times per week, are who will be interviewed and in what order, according to an intelligence source close to the ongoing case. Emails released by the State Department have already shown Clinton and several key aides used the personal, unsecured network to send more than 1,000 messages which have been deemed classified.

“In a case like this you get one shot at the queen,” the source, who was not authorized to speak on the record, said referring to Clinton, the former secretary of state and current front-runner for the Democratic presidential nomination. “The pressures are enormous on the agents, as the case has to be airtight and perfect.”

“In a case like this you get one shot at the queen.”

- Source with knowledge of investigation

Comey and Lynch are likely involved in daily briefings on the status of the explosive investigation, said Ron Hosko, former assistant director of the FBI’s criminal investigative division.

“This in an incredibly high stakes, high-wire act,” Hosko said. “Timing is of the essence, but being right is absolutely critical. Comey must be the one to make the case that the law has been broken and a prosecution is recommended.”

Nearly a dozen people who worked with Clinton at State, as well as others linked to the Clinton family’s nonprofit foundation have received, or are expected to receive, formal interview requests from the bureau, the source told Fox News. The Los Angeles Times reported Sunday that the FBI was setting up interviews with Clinton’s closest associates and would likely seek an interview with her.

“The authority for these formal interview requests by the Bureau is granted by the Attorney General,” the source added.

The formal interview requests are now being rapidly organized to set a time, date and place for the individuals to speak with federal agents about how their names have surfaced in the FBI’s ongoing criminal investigation. The interviews would not require any statements under oath, and subjects could decline them.

As the interviews evolve, the FBI, as first reported by Fox News last fall, will explore possible violations of Criminal Code section 1001, which covers "statements or entries generally," and can be applied when an individual makes misleading or false statements that cause federal agents to expend additional resources and time. Legal experts, as well as a former FBI agent, told Fox News Section 1001 could apply if Clinton, her aides or attorney were not forthcoming with FBI agents about her emails, classification and whether only non-government records were destroyed.

High-profile names convicted of violating Section 1001 include Martha Stewart, as well as former CIA Director David Petraeus.

Clinton recently insisted to Fox News’ Bret Baier during a town hall that neither she nor her lawyers have been formally notified that they are targets of an FBI investigation.

“Absolutely not,” Clinton said.

But such formal notification typically comes at the end of a process that sometimes spans months or even years of investigation, and even then only if it is determined that a subject’s activities likely merit prosecution.

Former Clinton campaign staffer and State Department information technology specialist Bryan Pagliano, who installed Clinton’s private server, was granted immunity by the Justice Department and is cooperating with the FBI.

“His importance as a witness cannot be underestimated,” a source told Fox News.

Pagliano has first-hand knowledge of who held and used accounts on the server from Clinton’s dealings in politics, philanthropy and private enterprise.  Understanding how these worlds intersected is “causing rats to leave the ship and others to sweat blood,” said the source. 

Who was doing what while getting paid by whom is key to the ongoing criminal probe, as the FBI’s No. 1 priority is ferreting out public corruption. Putting the pieces together is a challenge for federal investigators and investigative journalists.

Key Clinton aide Huma Abedin told the State Department in a July 5, 2013, letter that, “in addition to my work for the Department of State, I performed work for three others.”

Those jobs included working during parts of 2012 and 2013 for the Clinton-allied firm Teneo Holdings, which paid Abedin $105,000 even as she earned another $135,000 as a State Department “consultant.” Teneo, which was founded by longtime Clinton insider Doug Band, “advised clients on communications and investor relations for 10 different merger and acquisition deals worth a total of over $60 billion,” according to Fortune magazine.

In the same letter, Abedin stressed that “it is my understanding that Teneo does not conduct business with the Department of State. I also was not asked nor did I provide insights about the Department, my work with the Secretary or any government information to which I may have had access.”

The Clinton Foundation, founded in 1997, before President Bill Clinton left the White House, was renamed the “Bill, Hillary and Chelsea Foundation” six weeks after Hillary Clinton left the State Department in February 2013. Abedin worked for the foundation before and after it was renamed.

Critics, including Republican lawmakers, have suggested that Clinton may have used her influence as Secretary of State to reward donors to the foundation, which Hosko believes is an aspect of the email investigation.

“I am certain the FBI is looking at the nexus of State and the business of the foundation enrichment,” Hosko said. “Is there a shell game being played out on a global grand scale that creates a challenging paper trail?”

Pamela K. Browne is Senior Executive Producer at the FOX News Channel (FNC) and is Director of Long-Form Series and Specials. Her journalism has been recognized with several awards. Browne first joined FOX in 1997 to launch the news magazine “Fox Files” and later, “War Stories.”