Classified emails on Hillary Clinton's personal server, and a back-up copy on a thumb drive held by her lawyer David Kendall, appear to be a violation of the U.S. code governing the unlawful removal and storage of classified information, according to a leading national security lawyer. 

"In most situations like this you'd expect that a warrant would be issued and that the Marshals and the feds -- FBI, somebody would go and get that thumb drive and take it somewhere where it would be considered safe by the government," said Edward MacMahon Jr., an attorney who has handled major national security cases including the leak investigation of former CIA officer Jeffrey Sterling. 

Under 18 USC 1924, the unlawful removal and storage of classified information is described as when a person "knowingly removes such documents or materials without authority and with the intent to retain such documents or materials at an unauthorized location." The law sets punishment of a fine or prison term of "not more than one year." 

Attorney General Loretta Lynch made no commitment Friday to secure the classified information. "The inspectors general for the State Department and at least one other IG are reviewing how material was handled," she said. "We will review it as we review all referrals to us and take whatever steps are appropriate, if any, at this time." 

Fox News is told the information on Clinton's emails came from the National Security Agency, the Defense Intelligence Agency, and the National-Geospatial Agency, as well as the Office of the Director of National Intelligence and the Central Intelligence Agency. Dozens of additional emails released by the State Department Friday were retroactively classified, some as recently as Thursday. 

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A CIA spokesperson had no public comment, and the ODNI referred calls to the intelligence community inspector general, who could not comment on the intelligence's source. 

The details about classified and sensitive material are putting new pressure on Clinton to turn over her server and thumb drive for inspection. It was revealed last week that intelligence community and State Department watchdogs warned potentially "hundreds" of classified emails were on the system. Clinton has said all along she never sent or received information that was classified at the time. 

But the revelation that her attorney has a thumb-drive back-up copy on top of Clinton's personal server at her home in Chappaqua, N.Y., strongly suggests a double standard in the application of the law is at play -- as former CIA Director David Petraeus was prosecuted for removing classified information in his personal black notebooks, improperly sharing it with his biographer who had a security clearance, and storing the notebooks at his Virginia home, rather than a secure facility. 

Court documents in that case said the FBI "executed a court-authorized search warrant at the PETRAEUS Residence and seized the Black Books from an unlocked desk drawer in the first-floor study of the PETRAEUS Residence." 

A State Department spokesman told Fox News that Clinton's lawyer has "clearance. We've provided the lawyers with instructions regarding appropriate measures for physically securing the documents and confirmed via a physical security expert that they are taking those measures." Fox News was told the thumb drive is being held in a safe, but the State Department statement did not address the issue that classified information should never have been on the private server, or the thumb drive, and stored outside of a secure government facility. 

At Friday's press briefing, department spokesman Mark Toner also said comparing the Clinton and Petraeus situations is "apples to oranges." Toner denied that any laws had been broken. 

"There are rules that guard how [classified information is] supposed to be ... with how information is supposed to be stored and requires that it be handled in what's called a SCIF mostly -- a classified information facility with only limited access -- certain people can get into it," MacMahon said. 

A source close to the intelligence community inspector general said they are increasingly confident the server and thumb drive will be physically recovered. 

In a letter to FBI Director James Comey and Secretary of State John Kerry, Republican Sen. Chuck Grassley, R-Iowa, asked why the FBI had not acted as classified information has not been physically secured according to the statute.   

He cited recent inspectors general warnings that classified information was found in a sample of her emails, and said, "These recent revelations raise important questions about the role the Federal Bureau of Investigation (FBI) has taken and will continue to take in this matter." 

He noted that "a notification from the IC indicates that these classified emails existed on a thumb drive and may exist on a server," citing a briefing by inspectors general in saying Kendall "was in possession of the thumb drive at the time of the notice to the FBI and other IC components." 

He added, "This raises very serious questions and concerns if a private citizen is somehow retaining classified information. Accordingly, please explain whether Mr. Kendall had the requisite security clearance and authorization to be the custodian of classified national security information. If not, please explain what steps the FBI has taken or plans to take to secure and prevent further dissemination of the classified information contained on the thumb drive." 

A senior government official, such as a secretary of state with a high level security clearance, agrees to safeguard classified information -- that includes the use of a SCIF, which stands for sensitive compartmentalized information facility. In almost every case, a SCIF is build right into the home, and then removed after their term has concluded. 

After he resigned from CIA in 2012, Petraeus' home was raided shortly after his CIA SCIF was removed. 

"The crime of improperly storing classified information is actually a misdemeanor," MacMahon said. "Most of the people that plead guilty to those crimes plead to misdemeanors, they lose security clearances they have to go through the whole criminal justice process which is no fun, but, what we don't know is what she did -- who is she emailing this information to?" 

Fox News' Lucas Tomlinson and Matthew Dean contributed to this report. 

Catherine Herridge is an award-winning Chief Intelligence correspondent for FOX News Channel (FNC) based in Washington, D.C. She covers intelligence, the Justice Department and the Department of Homeland Security. Herridge joined FNC in 1996 as a London-based correspondent.