Follow the latest news on the leak of classified intelligence documents.

The 21-year-old National Guard airman was frantic as he joined a call with members of a small online gamer community that has improbably ended up at the center of a federal investigation into a major U.S. security breach.

It sounded as if the airman, Jack Teixeira, was in a speeding car, said a member of the group who uses the screen name Vahki.

“Guys, it’s been good — I love you all,” Airman Teixeira said, Vahki recounted. “I never wanted it to get like this. I prayed to God that this would never happen. And I prayed and prayed and prayed. Only God can decide what happens from now on.”

On Thursday, the F.B.I. arrested Airman Teixeira, an hour and a half after The New York Times identified him as the administrator of the online group, Thug Shaker Central, where a cache of leaked intelligence documents that riveted the world for a week first appeared.

It was Airman Teixeira, a member of the Massachusetts National Guard, his friends in the group said, who somehow obtained the classified documents and posted them to the group. From there, they eventually spilled into the open, potentially compromising U.S. intelligence gathering and damaging relations with allies.

In interviews, members of Thug Shaker Central said their group had started out as a place where young men and teenage boys could gather amid the isolation of the pandemic to bond over their love of guns, share memes — sometimes racist ones — and play war-themed video games.

But Airman Teixeira, who one member of the group called O.G. and was also its unofficial leader, wanted to teach the young acolytes who gravitated to him about actual war, members said.

And so, beginning in at least October, Airman Teixeira, who was attached to the Guard’s intelligence unit, began sharing descriptions of classified information, group members and law enforcement officials said, eventually uploading hundreds of pages of documents, including detailed battlefield maps from Ukraine and confidential assessments of Russia’s war machine.

His goal, group members said, was both to inform and impress.

Airman Teixeira’s access to secret information and his ability to know about major global events before they appeared on front pages stoked the curiosity of the group, which numbered 20 to 30 people.

“Everyone respected O.G.,” Vahki said in an interview. “He was the man, the myth. And he was the legend. Everyone respected this guy.”

What Airman Teixeira was not, Vahki said, was a whistle-blower in the vein of Edward Snowden and Chelsea Manning, whose outrage over perceived injustices led them to break the law and reveal closely held government secrets.

The secret documents in the news now, Airman Teixeira’s friends said, were never meant to leave their small corner of the internet.

“This guy was a Christian, antiwar, just wanted to inform some of his friends about what’s going on,” said Vahki, a 17-year-old recent high school graduate who identified himself by the screen name he used. “We have some people in our group who are in Ukraine. We like fighting games; we like war games.”

Now, their world is crumbling around them.

A New York Times report last week about the discovery of classified Ukraine war documents circulating online prompted the Pentagon to open an investigation, followed by national security officials racing to close down access to sensitive materials and reassure distraught allies that the U.S. government was still in control of its secrets.

The extent of the damage caused by the leak is not yet fully known.

The materials Airman Teixeira is accused of sharing revealed how deeply the Russian government had been penetrated by U.S. and allied intelligence agencies, which gained the ability to provide near-real-time information to the Ukrainians about planned Russian strikes.

They also showed that America’s spy services were eavesdropping on allies like Israel and South Korea, as well as the Ukrainian leadership, embarrassing revelations that could erode trust at a time when Washington was trying to present a unified front in the conflict with Moscow.

On Thursday, F.B.I. agents wearing helmets and flak jackets and carrying military-style assault rifles descended on the home where Airman Teixeira lived with his mother and took him into custody.

It all started innocuously, his online circle of friends said. As the pandemic closed schools and workplaces, plunging the world into isolation, the young men in Thug Shaker Central gravitated to one another online, finding solace in their shared interests, mostly video games like Project Zomboid, in which players try to survive in a post-apocalyptic Kentucky overrun by zombies.

They first met on a server called Oxide Hub, a large military-focused community on Discord, a social media platform popular among gamers — but abandoned it in favor of a closed, tighter-knit group.

They did not hide some of their extreme ideological views. On Steam, another popular gamer platform, members of the group traded racist and antisemitic epithets and appeared in other groups featuring Nazi iconography.

Vahki admitted to retweeting racist memes. “There’s no point hiding it,” Vahki said. “I’m not a good person.”

Airman Teixeira named the group Thug Shaker Central, which members acknowledged was an inside joke based on an internet meme. The investigative collective Bellingcat first reported that the group was the original source of the leaks. The Washington Post also reported details about the group.

Airman Teixeira, the friends said, was popular online and known as an active creator of memes. Online, he went by a number of different screen names, among them TheExcaliburEffect, jackdjdtex and TexKilledYou.

He grew up in North Dighton, Mass. Photographs from family members’ social media accounts show him curled up with his family’s two dogs, riding ATVs and wearing Boston Celtics gear. His mother posted pictures of his family members in the military every Veterans Day.

Following their footsteps, the young man joined the military after he graduated from Dighton-Rehoboth Regional High School in the summer of 2020, missing his graduation ceremony to attend his basic training obligations at Lackland Air Force Base in Texas. He finished his technical training the following year and officially entered active duty with the Massachusetts Air National Guard’s 102nd Intelligence Wing on Oct. 1, 2021.

Among the dozens of birthday wishes and baby pictures of Airman Teixeira on his sister’s social media feeds was a clue that he might be the leaker. One photograph captured a kitchen countertop that appeared identical to the surface on which the classified documents were photographed.

In addition to games, Airman Teixeira’s online group also shared an interest in guns. Vahki said he was a good marksman, and records unearthed by The Times show that he exchanged gun equipment with his fellow gamers.

“We’re gunners, we’re gear nerds,” Vahki said, adding that group members have spent hundreds of dollars on gear both in the virtual world and in real life.

But Airman Teixeira also began posting a different sort of content.

It started as long daily memos with complicated and, at times, confusing summaries of international events that members of the group found difficult to follow. Sometimes he would admonish his younger friends for not taking the information seriously, Vahki said.

Around October last year, his frustration led him to start posting original documents, including detailed battle maps from the war in Ukraine marked “TOP SECRET.” From October to March, Vahki said, the airman posted about 350 documents to the group.

The documents might have remained confined to Thug Shaker Central were it not for a member of the group named Lucca, a 17-year-old from California, who might not have fully grasped the gravity of the documents he had been given access to.

On March 2, Lucca was involved in a conversation about the Ukraine war in a public Discord group called #War-Posting when he published several dozen documents from the cache that had been uploaded to Thug Shaker Central.

For a month, the documents bounced around esoteric chat groups, including one popular with players of the online game Minecraft and another for fans of a moderately popular British YouTuber. They went seemingly unnoticed by anyone who understood their importance until early April, when some of the documents began appearing on the Telegram messaging app channels of supporters of Russia’s war against Ukraine.

As the news began to spread, Airman Teixeira started closing down his online accounts and bidding farewell to online friends.

“He was very freaked out,” Vahki said. “This isn’t something like an ‘oopsie-daisy — I’m going to be reprimanded.’ This is life-in-prison type stuff.”

Kitty Bennett and Sheelagh McNeill contributed research.