WASHINGTON — They risk imprisonment or death stealing the secrets of their own governments. Their identities are among the most closely protected information inside American intelligence and law enforcement agencies. Losing even one of them can set back U.S. foreign intelligence operations for years.

Clandestine human sources are the lifeblood of any espionage service. This helps explain the grave concern within U.S. agencies that information from undercover sources was included in some of the classified documents recently removed from Mar-a-Lago, the Florida home of former President Donald Trump — raising the prospect that the sources could be identified if the documents got into the wrong hands.

Trump has a long history of treating classified information with a sloppiness few other presidents have exhibited. And the former president’s cavalier treatment of the nation’s secrets was on display in the affidavit underlying the warrant for the Mar-a-Lago search. The affidavit, released in redacted form on Friday, described classified documents being found in multiple locations around the Florida residence, a private club where both members and their guests mingle with the former president and his coterie of aides.

Nothing in the documents released on Friday described the precise content of the classified documents or what risk their disclosure might carry for national security, but the court papers did outline the kinds of intelligence found in the secret material, including foreign surveillance collected under court orders, electronic eavesdropping on communications and information from human sources — spies.

Trump and his defenders have claimed he declassified the material he took to Mar-a-Lago. But documents retrieved from him in January included some marked “HCS,” for Human Intelligence Control System. Such documents have material that could possibly identify CIA informants, meaning a general, sweeping declassification of them would have been, at best, misguided.

“HCS information is tightly controlled because disclosure could jeopardize the life of the human source,” said John B. Bellinger III, a former legal adviser to the National Security Council in the George W. Bush administration. “It would be reckless to declassify an HCS document without checking with the agency that collected the information to ensure that there would be no damage if the information were disclosed.”


CIA espionage operations inside numerous hostile countries have been compromised in recent years when the governments of those countries have arrested, jailed and even killed the agency’s sources.

Last year, a top-secret memo sent to every CIA station around the world warned about troubling numbers of informants being captured or killed, a stark reminder of how important human source networks are to the basic functions of the spy agency.

FBI: Trump mixed top secret docs with magazines, other items

When FBI agents in May went through the 15 boxes of material turned over to the National Archives by Trump in January, a year after he left office, they quickly determined that the boxes contained 184 documents marked as classified, including some labeled HCS — an especially troublesome revelation in the eyes of intelligence experts.

“It is among the most sensitive information relating to human intelligence sources and very tightly held at the CIA,” said George Jameson, a former senior CIA officer and lawyer. “A compromise could result in harm to the source and the source’s information.”

An intelligence document marked HCS will contain details about the source of the information. Often such descriptions are very general, noting if a “clandestine source” has direct or secondary knowledge of the intelligence presented. But sometimes there are more direct descriptions to help policymakers properly assess the information, details that could allow people reading the document to identify the source — a prime reason the spy agency seeks to tightly control HCS documents.


The HCS designation is “used to protect exceptionally fragile and unique” human intelligence operations and methods “that are not intended for dissemination outside of the originating agency,” according to a 2013 directive from the Office of the Director of National Intelligence.

According to former officials, documents marked HCS have special handling requirements to make sure they are stored properly and not reviewed by people who are not cleared to see them.

“Although the president generally received finished intelligence that included HCS reporting, this would include source descriptions and context to establish the information’s reliability, details that would enable an adversary to narrow down from whom, and where, the secrets came,” said Douglas London, a former CIA officer who was a top counterterrorism official during the Trump administration. “The more sensitive the information, the fewer the suspects or technical vulnerabilities for the adversary to investigate.”

In addition to the HCS markings, some of the documents were marked FISA, indicating information collected under the Foreign Intelligence Surveillance Act.

“What this tells us is that there was possibly something from human beings, from spies, possibly something involving foreigners who are the only ones targeted under FISA and potentially there is very sophisticated sensitive information involved here,” said Glenn S. Gerstell, the former general counsel of the National Security Agency.

Ultimately, Gerstell said, understanding how sensitive any of the documents are, and what sources might be compromised, requires the documents to be examined by the Office of the Director of National Intelligence. Such an examination is one reason the Justice Department and the FBI conducted the search at Mar-a-Lago to collect the material.

Until more about the nature of the documents is publicly known, it is impossible to tell what, if any damage was done. But former officials stressed that counterintelligence experts often will take measures to protect sources or change collection methods if they believe a classified document could have been viewed by people not authorized to see it.

“It is a principle of counterintelligence that when you believe a code or classified material has been possibly compromised you have to assume the worst,” Gerstell said. “It is a powerful reason to know what is in the documents and who had access.”