A member of the Massachusetts Air National Guard is expected to be arrested soon in connection with the leaking of classified documents that were posted online, a source says

Law enforcement arrested Jack Teixeira Thursday in connection with the leaking of classified documents that have been posted online, according to a US official familiar with the matter. 

Teixeira, 21, is a member of the Massachusetts Air National Guard. His arrest comes following a fast-moving search by the US government for the identity of the leaker who posted classified documents to a social media platform popular with video gamers.

Teixeira was first identified by The New York Times Thursday ahead of his arrest as the leader of the group where a trove of classified documents was posted.

Law enforcement is expected to soon arrest a member of the Massachusetts Air National Guard in connection with the leaking of classified documents that have been posted online, according to a law enforcement source.  

The guardsman is 21-year-old Jack Teixeira, according to the New York Times, which reported that he is the leader of an online gaming group where a trove of classified documents was posted.

Some background: The FBI had narrowed the number of people who they believe could be responsible for the leaks and have been conducting interviews in recent days, two people briefed on the matter said earlier.

While there's a large number of people who had access to the documents, investigators have been able to home in on a small number for closer scrutiny, thanks to the forensic trail left by the person who posted the documents. Investigators are working on building a case for prosecution, people familiar with the matter say. 

A major leak of classified Pentagon documents has rattled US officials, members of Congress and key allies in recent days.

Now a criminal investigation is being led by the FBI’s Washington field office to find who is responsible. The FBI had narrowed the number of people who could have leaked the information and have been conducting interviews in recent days, two people briefed on the matter said earlier. 

What we know about what happened: The documents appeared online last month on the social media platform Discord, according to screenshots of the posts reviewed by CNN.

The posts are photos of crumpled documents laid on top of magazines and surrounded by other random objects, such as zip-close bags and Gorilla Glue. It is as if they had been hastily folded up and shoved into a pocket before being removed from a secure location, a source familiar with these kinds of documents told CNN.

A Discord spokesperson confirmed in a statement Sunday that they are cooperating with law enforcement on the investigation.

Those documents discovered on Friday all bore classified markings, some top secret — the highest level of classification.

Some of the documents, which US officials say are authentic, expose the extent of US eavesdropping on key allies, including South Korea, Israel and Ukraine. Others discuss Russia's war in Ukraine.

Ukrainian servicemen fire at Russian positions in the Donbas region last month. (Aris Messinis/AFP/Getty Images)

Leaked Pentagon documents contain a wide range of highly classified information – providing a rare window into how the United States spies on allies and adversaries alike.

CNN has reviewed 53 leaked documents, all of which appear to have been produced between mid-February and early March.

Some of the documents, which US officials say are authentic, expose the extent of US eavesdropping on key allies, including South Korea, Israel and Ukraine.

On Russia and Wagner Group: Others reveal the degree to which the US has penetrated the Russian Ministry of Defense and the Russian mercenary organization Wagner Group, largely through intercepted communications and human sources, which could now be cut off or put in danger.

On Ukraine's military and Zelensky: Still, others divulge key weaknesses in Ukrainian weaponry, air defense, and battalion sizes and readiness at a critical point in the war, as Ukrainian forces gear up to launch a counteroffensive against the Russians – and just as the US and Ukraine have begun to develop a more mutually trusting relationship over intelligence-sharing.

One document reveals that the US has been spying on Ukrainian President Volodymyr Zelensky. That is unsurprising, said a source close to Zelensky, but Ukrainian officials are deeply frustrated about the leak.

The US intelligence report, which is sourced to signals intelligence, says that Zelensky in late February “suggested striking Russian deployment locations in Russia’s Rostov Oblast” using unmanned aerial vehicles since Ukraine does not have long-range weapons capable of reaching that far.

Signals intelligence includes intercepted communications and is broadly defined by the National Security Agency as “intelligence derived from electronic signals and systems used by foreign targets, such as communications systems, radars, and weapons systems.”

On South Korean officials: Yet another document describes, in remarkable detail, a conversation between two senior South Korean national security officials about concerns by the country’s National Security Council over a US request for ammunition.

The officials worried that supplying the ammunition, which the US would then send to Ukraine, would violate South Korea’s policy of not supplying lethal aid to countries at war. According to the document, one of the officials then suggested a way of getting around the policy without actually changing it – by selling the ammunition to Poland.

Read more.

The Pentagon is seen from the air in this March 2022 file photo. (Joshua Roberts/Reuters/File)

The Pentagon has begun to limit who across the government receives its highly classified daily intelligence briefs following a major leak of classified information discovered last week.

Some US officials who used to receive the briefing materials daily have stopped receiving them in recent days, sources familiar with the matter told CNN, as the Pentagon’s Joint Staff continues to whittle down its distribution lists.

The Joint Staff, which comprises the Defense Department’s most senior uniformed leadership that advises the president, began examining its distribution lists immediately after learning of the trove of leaked classified documents – many of which had markings indicating they were produced by the Joint Staff’s intelligence arm, known as the J2.

All the email lists have been reviewed, a senior defense official said, and some restrictions may only be temporary. Everyone on the lists had proper clearance, but not everyone needs to receive that information daily, the official added.

Pentagon spokesperson Brig. Gen. Pat Ryder in a Wednesday interview with News Nation that the Pentagon is looking at “mitigation measures in terms of what we can do to prevent potential additional unauthorized leaks.”

The leaked documents have exposed what officials say are lingering vulnerabilities in the management of government secrets, even after agencies overhauled their computer systems following the 2013 Edward Snowden leak, which exposed the scope of the National Security Agency’s intelligence gathering apparatus.

It is unlikely, however, that those safeguards would have prevented the most recent leak, sources said. The documents that circulated online appear to have been printed largely from briefing books that staffers spend hours putting together for senior officials on the Pentagon’s Joint Staff.

A 21-year-old Massachusetts Air National Guardsman has been identified by The New York Times as the leader of an online gaming chat group where a trove of classified documents — which contain information about the war in Ukraine — was posted. 

The Times reported Thursday that FBI investigators want to talk to the service member and believe he has information relevant to the ongoing investigation into the leak.

CNN has not independently verified the identity of the chat leader or the FBI’s interest in talking with him. 

Earlier Thursday, President Joe Biden appeared to suggest that the US government is close to identifying the leaker.

CNN has previously reported that the Army Criminal Investigation Division is also “assisting the DoD in their investigation” of the leak, Jeffrey Castro, a spokesman for the division, told CNN.

On Wednesday, the Washington Post reported that the person behind the leak worked on a military base and posted sensitive national security secrets in an online group of acquaintances.

The FBI has narrowed the number of people who they believe could be responsible for leaks of classified US documents and have been conducting interviews in recent days, two people briefed on the matter said. 

While there is a large number of people who had access to the documents, investigators have been able to home in on a small number for closer scrutiny, thanks to the forensic trail left by the person who posted the documents. Investigators are working on building a case for prosecution, the people familiar with the matter say. 

The FBI believes they are close to identifying the person behind the leak.

The leaked documents posted to social media, some of which have been obtained by CNN, include detailed intelligence assessments of allies and adversaries alike, including on the state of the war in Ukraine and the challenges both Kyiv and Moscow face as the conflict appears stuck in a stalemate in the months ahead.

Another source familiar with the criminal investigation at this point said that they expect it’ll move along much more quickly than the Pentagon’s damage assessment. The source also said that the FBI is getting closer to identifying a suspect.

CNN has previously reported that the Army Criminal Investigation Division is also "assisting the DoD in their investigation" of the leak, according to Jeffrey Castro, a spokesperson for the division. It is unclear if the alleged leaker works within the US Army.

The Washington Post reported Wednesday that the person behind the massive leak of classified US military documents worked on a military base and posted sensitive national security secrets in an online group of acquaintances. CNN has not been able to independently verify the reporting.