Unanswered questions are what officials call gaps—a lack of information or intelligence that render judgments incomplete. FBI Director James Comey last week took the extraordinary step of re-opening the FBI's investigation of Hillary Clinton's private email server in a bid to close some of those gaps—11 days before Americans go to the polls to elect the next president.
Comey wrote to congressional leaders on October 28 to "supplement" earlier testimony in which he said the FBI had completed its investigation of Clinton.
An unrelated FBI sex crime investigation into former congressman Anthony Weiner, husband of Clinton campaign vice chair Huma Abedin, produced new emails "that appear to be pertinent to the investigation," Comey said.
Investigators briefed Comey on the new emails on October 27 and he agreed to reopen the probe in order to check whether the emails contain classified information and whether they are important to the original investigation.
"Although the FBI cannot yet assess whether or not this material may be significant, and I cannot predict how long it will take us to complete this additional work, I believe it is important to update your committees about our efforts in light of previous testimony," he stated.
The letter gave no further explanation. However, based on past FBI statements and documents, the probe likely involves one of two areas of the investigation: New information on the government secrets transmitted in emails or new evidence of foreign hacking.
The Los Angeles Times, quoting Comey "confidants," reported the FBI director wrote the letter under pressure from multiple fronts. The fronts included the Justice Department, current and former FBI agents, and Democrats and Republicans. Comey's letter was an attempt to deal with the politically charged Clinton email probe in a transparent manner, according to the report.
The reopening of the investigation raises new questions about whether the FBI conducted the original inquiry properly, or closed it before all the facts had been learned.
FBI investigation documents made public under pressure from Congress revealed that there had been several shortcomings to the original probe.
One FBI document in the case states the probe was launched to determine if classified information was criminally mishandled and whether foreign intelligence services or governments accessed it.
The document says "investigative limitations"—namely the failure to obtain all the devices and computer components used by Clinton—"prevented the FBI from conclusively determining whether classified information transmitted and stored on Clinton's personal server systems was compromised via cyber intrusion or other means."
It noted that "hostile foreign actors" gained access to private emails Clinton had sent and received from an associate.
The FBI also said there were literal gaps—as opposed to a shortage of information—in Clinton emails between January and March 2009.
Moreover, the FBI was unable to study 13 mobile handheld devices and two iPads used by Clinton while secretary of state.
The year-long investigation began after the U.S. intelligence community's inspector general disclosed that 40 emails found on the Clinton private server contained classified intelligence information.
It was later revealed that among the secrets placed on the server and exchanged in unclassified and unsecure emails were top-secret methods used to order drone strikes. Other data involved secrets about North Korea's nuclear program.
The drone strike information was most concerning to intelligence officials. Failing to respond to the compromise threatened to undermine the government's large-scale secrecy and information classification system.
Information concerning target selection for drone strikes is classified above top secret in what are called Special Access Programs—compartments so sensitive that officials are permitted to lie in order to prevent their disclosure.
The investigation was completed within a year, and Comey went public with its findings in July. Included in the statement he made was the controversial recommendation that, although Clinton had been extremely careless and had likely met the "gross negligence" legal standard for the crime of mishandling classified information, he was not recommending prosecution.
Comey based the conclusion on his personal view that no reasonable prosecutor would take the case to a grand jury. The politicized Justice Department and Attorney General Loretta Lynch quickly accepted his decision.
Comey issued a statement on July 5 that revealed the investigation was limited to two areas. The first concerned whether classified information was stored or transmitted illegally while she was secretary of state from 2009 to 2013. The second involved whether foreign intelligence services or hackers stole the information, which, from a cyber security perspective, had effectively been placed in the open.
"Consistent with our counterintelligence responsibilities, we have also investigated to determine whether there is evidence of computer intrusion in connection with the personal e-mail server by any foreign power, or other hostile actors," he said.
Comey provided a qualified answer that "we did not find direct evidence" of a break-in by foreign cyber spies.
The FBI probe involved interviews with people who handled the server and people who sent the emails. It also involved technical analysis of the available computer systems.
With the presidential race tightening in the final days, the reopening of the Clinton email investigation was a political bombshell.
For Clinton, who has battled questions about whether she has the integrity to be president, the news of the reopened FBI investigation hit hard. Clinton and her campaign called for the FBI to release more information about the action, and Democratic supporters accused Comey of seeking to influence the outcome of the election. On Sunday, Clinton tweeted that the FBI had not reopened the investigation and stated that the new emails were not hers.
"Yesterday [sic], FBI Director Comey bowed to partisan pressure and released a vague and inappropriate letter to Congress. What you need to know," she stated.
The news energized the campaign of Republican nominee Donald Trump. After the story broke, Trump posted a message to Twitter that stated "we must not let #CrookedHillary take her CRIMINAL SCHEME into the Oval Office #DrainTheSwamp." And on Sunday, Trump stated: "Hillary and the Dems loved and praised FBI Director Comey just a few days ago. Original evidence was overwhelming, should not have delayed!"
Unless Comey is pressured to disclose more information, the investigation likely will go beyond Election Day.