Manafort jurors yet to reach verdict. Should Mueller be worried?

As deliberations dragged into a fourth day in the financial crimes trial of former Trump campaign chairman Paul Manafort, speculation about how to interpret the jury's pace grew more frenzied. But the closed nature of the proceedings meant even seasoned veterans could only guess.

"Certainly each passing day gives the defense more reason to hope that at least one juror remains unpersuaded by the government's case," former federal prosecutor Robert Mintz told ABC News. "If you are the prosecution, you may be concerned, but you are certainly not yet alarmed."

Jurors began deliberating last Thursday morning. In the days since, the panel has largely kept to themselves in a secluded room on the ninth floor of the federal district courthouse in Alexandria, Virginia.

Special counsel Robert Mueller and his team of prosecutors secured an 18-count indictment on tax- and bank-fraud charges against Manafort, who faces more than 300 years in prison if found guilty on all counts, though legal experts tell ABC News that a far lesser sentence would be expected.

Manafort, 69, has pleaded not guilty to all charges.

An exception to the jury's closed-off deliberation came last Thursday afternoon, when jurors sent a note with questions to Judge T.S. Ellis, the federal judge overseeing Manafort's Virginia case. In their note, jurors asked Judge Ellis to define "reasonable doubt."

Ellis clarified to jurors that the prosecution is not required to find "guilt beyond all possible doubt," but defined reasonable doubt as a "doubt based on reason."

Just before noon on Tuesday, jurors sent a question to the judge asking how to proceed if the panel could not come to a consensus on a single count. Ellis told the court that jurors' question "is not unusual in a jury trial," and it was not immediately clear whether jurors had reached a unanimous verdict on the other counts.

Ellis suggested that jurors be willing to "re-examine and reconsider" their positions and deliberate with "candor and frankness." After less than ten minutes in the courtroom, Ellis sent jurors back to continue deliberating.

After Monday's session concluded, Manafort's lead defense attorney Kevin Downing told ABC News that his client "is very happy to hear" that jurors would return for a fourth day of deliberation, and that he believes the continued deliberations are favorable for the defense.

But legal experts offered a more measured response.

"Juries generally take their responsibilities very seriously and complicated, document intensive cases like this often require time to review and consider all of the evidence," Mintz told ABC News. "The real question both teams of lawyers are asking themselves is whether this delay is a function of true disagreements brewing inside the jury room or merely a result of a diligent jury simply doing its job."

Prosecutors entered 388 exhibits into evidence for the jury to review - with one exhibit alone totaling more than 700 pages. A careful consideration of these documents may understandably prolong any timeline for reaching a verdict. Jurors asked the judge of they could have a guide of which exhibits were tied to each charge, but Ellis declined.

A former Eastern District of Virginia prosecutor told ABC News that jurors are likely being conscientious, but added that "If there's no verdict or questions by the end of Tuesday, then there may be some concern for the government."

Deliberations are expected to continue until the jury advises the court that they have reached a verdict, have a question for the judge, or are hopelessly deadlocked.

If the jury says they are unable to reach a verdict, that does not necessarily mean their deliberations are over.

"Even then, the Judge is permitted to give what is called an Allen charge (based on a US Supreme Court case Allen v U.S. from 1896) in which the judge urges jurors to continue to deliberate and try to reach a unanimous verdict," Mintz told ABC News.

Meanwhile, outside the courthouse a collection of defense attorneys, prosecutors, journalists, protesters and curious onlookers remain in limbo, anxiously awaiting the jury's decision of Paul Manafort's fate.

Only the six men and six women in that secluded room on the courthouse's ninth floor know how long that will take.