The FBI is also trying to determine whether foreign powers, especially China or Russia, gained access to Clinton’s private server, although at this point, any security breaches are speculation.

Share story

WASHINGTON — FBI agents investigating Hillary Rodham Clinton’s private email server are seeking to determine who at the State Department passed highly classified information from secure networks to Clinton’s personal account, according to law-enforcement and diplomatic officials and others briefed on the investigation.

To track how the information flowed, agents will try to gain access to the email accounts of many State Department officials who worked there while Clinton was secretary of state, the officials said. State Department employees apparently circulated the emails on unclassified systems in 2009 and 2011, and some were ultimately forwarded to Clinton.

They were not marked as classified, the State Department has said, and it is unclear whether its employees knew the origin of the information.

The FBI is also trying to determine whether foreign powers, especially China or Russia, gained access to Clinton’s private server, although at this point, any security breaches are speculation.

Law-enforcement officials have said that Clinton, who is the front-runner for the 2016 Democratic nomination for president, is not a target of the investigation, and she has said there is no evidence that her account was hacked.

There has also been no evidence that she broke the law, and many specialists believe the occasional appearance of classified information in her account was probably of marginal consequence.

A spokesman for Clinton said in a statement on Friday that she “took the handling of classified information very seriously.”

“She always received classified materials in secure settings, either by phone, video conference, on paper or in person,’‘ said the spokesman, Nick Merrill. “If, however, some material unknowingly ended up somewhere on the State Department’s unclassified email system, we want to continue to be as helpful as possible in getting to the bottom of that.’‘

This week, the inspector general of the nation’s intelligence agencies, I. Charles McCullough III, informed members of Congress that Clinton had “top secret” information, the highest classification of government intelligence, in her account.

Some of that information, according to a memorandum the inspector general sent to the heads of the Senate and House intelligence and judiciary committees, may have come from a program called Talent Keyhole, which relies on satellite intercepts of conversations or imagery data. The program involves some of the most secure information in the intelligence agencies’ computer systems.

The investigation into Clinton’s emails has its roots in her decision to use only a private email account for her official business when she was secretary of state, an unorthodox decision that gave her some control over what was made public.

She faced criticism when her use of the account became known this year, and after deleting what she said were more than 31,000 personal emails, she turned over more than 30,000 work-related emails for the State Department to make public.

According to current and former State Department officials who worked with Clinton, almost all classified information was routed to classified government servers in her office, where it was printed out for her review. Her predecessor, Condoleezza Rice, often operated the same way, preferring to read classified data in printed form.

Sen. Dianne Feinstein of California, the ranking Democrat on the Senate Intelligence Committee, said in a statement Thursday in response to what she said were “allegations about Clinton’s emails” that “none of the emails alleged to contain classified information were written by Secretary Clinton” and that “none of the emails alleged to contain classified information include any markings that indicate classified content.”