WASHINGTON — Jack Teixeira, the 21-year-old Air National Guardsman accused of releasing classified material on a social media site, will return to court on Wednesday for a pretrial detention hearing in Boston.

Prosecutors often reveal new details of their case against the accused at such a hearing, but only enough information to make their case that he is a potential flight risk, poses a danger to national security — or both — if he is released. (A filing earlier this week added a few minor facts, most notably that Mr. Teixeira, a member of the Massachusetts Air National Guard, once fired a vintage Soviet pistol.)

The more consequential legal step is an indictment, a document that would include a far more detailed description of his actions than has previously been made public, and a more specific accounting of the charges against him in connection with the fast-moving investigation into the leaked documents.

Here is what we know about the case against Airman Teixeira.

What classified documents is Airman Teixeira accused of taking?

Neither prosecutors nor national security officials yet know the full extent of the intelligence taken from the U.S. government’s classified systems. The material posted online primarily includes slides about the war in Ukraine created by the intelligence directorate of the Pentagon’s Joint Staff. But there is also highly classified material from the National Security Agency, the Central Intelligence Agency, the Defense Intelligence Agency and other spy agencies.

Many of the dozens of documents that have emerged so far are snapshots in time — bits of intelligence or overviews of the battlefield in Ukraine compiled on a particular day. But some of the material provides a level of detail about the strengths and weaknesses of the Russian and Ukrainian forces that American officials have been reluctant to discuss.

The documents were first posted on Discord, a social media platform popular among gamers, then shared more widely. Some were later altered and reposted on other social media.

What do investigators know about how the documents were taken?

Airman Teixeira worked as an information technology specialist and had administrative privileges on classified computer systems that appear to have allowed him access to a wide range of material, including briefing slides. But investigators are also trying to learn if he might have collected the material using less technologically sophisticated methods. Officials caution that the inquiry is in early stages and there is more to learn about how the airman might have gathered the material and removed it from the military base where he worked.

What is the Pentagon doing to mitigate future leaks?

The answer to that question will depend somewhat on what investigators learn about how he got access to this material. For now, intelligence agencies are not curbing their sharing of documents with the Pentagon. President Biden has ordered the Pentagon to limit the distribution of sensitive information, however. The Pentagon has also announced that it would review procedures across the Defense Department for using and securing the nation’s secrets.

How did investigators and the news media find Airman Teixeira?

Both the F.B.I. and news reporters found him in much the same way: by interviewing other members of Discord.

The members of the Thug Shaker Central Discord server who spoke with The New York Times did not reveal Airman Teixeira’s identity. But they shared some details about him, and reporters were able to find people on other video game forums connected to the known members of Thug Shaker Central, including Mr. Teixeira.

To be sure, the Federal Bureau of Investigation found him first. But investigators must go through legal hurdles, like obtaining court approval for a search warrant. The Times had a chance to knock on Airman Teixeira’s door a few hours before F.B.I. agents arrived to search his home.

Is this case radically different than other leak cases?

Airman Teixeira’s case bears some resemblance to other relatively recent leak cases in which people connected to the military or a spy agency used their access to acquire sensitive documents and posted them online or gave them to the news media.

But Chelsea Manning, who gave documents to WikiLeaks, and Reality Winner and Edward Snowden, who provided documents to the news media and other organizations, were trying to bring attention to things they thought the public needed to know. Airman Teixeira, however, is accused of sharing documents with a small group of acquaintances, rather than trying to reveal them to the wider public.

Will he be tried in Boston?

Justice Department officials are still considering whether to ask the court to move the case to the Eastern District of Virginia, a court where both prosecutors and public defenders have extensive experience handling cases involving classified secrets. While Airman Teixeira is accused of taking the documents from a military base in Massachusetts, much of that material was originally created by the Pentagon, which is in the Eastern District.