Earlier this year, an FBI investigation revealed 21-year-old Massachusetts Air National Guardsman Jack Teixeira had been responsible for one of the most damaging document leaks in U.S. history on the online chat room known as Discord.

Since then, the Washington Post and GBH’s FRONTLINE haveteamed up to investigate how the military missed so many red flags over Teixeira and how he was able to so easily access the documents. Their new documentary on the investigation, "The Discord Leaks," premieres tonight at 10 p.m. EST on PBS stations.

The Washington Post intelligence and national security reporter Shane Harris, one of the lead journalists for the story, joined GBH’s All Things Considered host Arun Rath to discuss the monthslong investigation. The following is a lightly edited transcript.

Arun Rath: So Jack Teixeira seems like a fairly nondescript kid growing up in Dighton, Massachusetts, but as you dig in, there are these awful, clear, massive red warning flags out in the open, including a plan to “shoot up his high school.”

Shane Harris: That’s right, yeah. This was actually an incident during his sophomore year in high school that was documented in a police report. A number of students complained to school officials that they had heard Teixeira talking about bringing weapons to school, including Molotov cocktails. One student said that Teixeira told him he had a Molotov cocktail in his backpack and wondered what the student would do if Teixeira threw it down the hallway. So they were pretty alarmed.

As police investigators started to look more deeply into this, they talked to other teachers and students who said that they, too, had heard him talk a lot about guns. The police also found that Teixeira had — according to students — a history of making threats toward Black people in particular and looking at images of gore and violence while he was at school and sharing them with other students.

It was a pretty troubling set of indicators that, I think, in our current context of school violence, clearly set off certain alarm bells with students and teachers, as well as his high school.

Rath: So there’s that out in the open. Then, you also track his radicalization through this platform, Discord. Let’s talk about his friend group on Discord; you’ve talked with several of them. This was originally a platform for gamers, but by the time Teixeira was on, how much had it become a haven for radicals?

Harris: Yeah, that’s right. He met many of these friends during the pandemic when a lot of these kids — and they were kids, many of them were teenagers at the time — met in this Discord server where they were all fans of military hardware, guns, gear and video games, and that drew them all together.

But over time, what happened was they began to share a lot of memes and jokes that were racist and antisemitic. They talked openly about doing violence to federal agents. They would joke about the best way to kill an ATF agent if they showed up at their door. The rhetoric became very dark and very violent, and I think some of these kids were perhaps saying these things to try and get a rise out of people or shock them.

But it became pretty clear to us as we really dug into this that Teixeira really did harbor some pretty suspicious views of the government; I think we would call them conspiracies. He believed that the government allowed mass shootings to happen as a pretext for tightening gun laws.

Some of these really radical and racist beliefs that he was expressing — according to friends that we talked to — he did believe these things. The server that they were in, this kind of chat space really hardened around his views, and as some described it to us, he kind of became a cult of personality in which a lot of these young kids looked up to Teixeira and tried to emulate him as well.

Rath: There’s so much stuff that is really jaw-dropping as we go through this hour. Let me put to you the question, which you air in the second half of this film, is: With so many big, bright red flags, how on Earth did Teixeira make it into the military, and how on Earth did he get security clearance?

Harris: I think it’s one of the most important questions in the film. I think the best answer that we found is that the military simply didn’t know about this part of Jack Teixeira’s life.

When someone applies for a security clearance — which he needed to do his job as a computer technician at an Air National Guard base in Massachusetts — investigators will ask that person to list their travel history, their financial history, personal contacts. They will often go and interview neighbors or friends, or maybe school or work associates. But they don’t require that the applicant disclose their social media activity. They don’t say, “Tell us if you’re on Discord and, if you are, what are the names of the servers that you’re hanging out in?”

Had they gone and talked to people who Jack Teixeira knew online — even one or two, and we talked to a lot more than that — I think that they would have immediately started to develop a picture of someone who is not necessarily the Jack Teixeira that was presented to them if you looked at only his offline connections.

Teixeira really did spend a huge part of his life online, so the Defense Department was essentially blind to that. They did not see a lot of these indicators. We do think that investigators were aware of the threats that he made at his high school. We don’t precisely know why they determined that that was not a significant enough negative piece of information to deny him a security clearance, but they really were missing the whole of Jack Teixeira because they did not see his online life.

Rath: One of the jaw-dropping moments in the film is when you reveal that he was actually caught at one point talking about the conditions at the base in Massachusetts that let him get away with this.

Harris: Right. He worked on this air base that’s for something called the 102nd Intelligence Wing. He worked inside an intelligence facility that is supposed to be a secure space; you can’t bring a cellphone or an electronic device. He worked on maintaining computer systems that connect to classified top-secret government and military computer networks on which there was just streams of intelligence moving all day about the war in Ukraine, about what the intelligence community knows about what Russia is doing, China, North Korea, Iran — so, really, just an entire vault of secrets.

Because he was a computer technician, he needed a top-secret clearance to be able to work on those networks, but it was his job not to read the information there. He was only supposed to be maintaining the equipment on which analysts and other people authorized could read the intelligence.

But his superiors caught him snooping around in documents and reading documents that he shouldn’t have been, and on four separate occasions, he was reprimanded for this. Superiors caught him taking notes on documents that he was reading and putting a note in his pockets, things that you just are never supposed to do. Certainly, someone who was working at a low-level computer job like Teixeira should not have been doing.

What was astonishing was that every one of these times that he was caught and reprimanded, no one pulled him off the line. No one said, “OK, we’re suspending your access here until we figure out what you’re up to.” In fact, one of the times after they caught him, they actually offered him a promotion to become an analyst so that he might have a legitimate reason to read classified information. He declined the training and just kept looking at documents during this time.

By the way, he is also, we think, leaking this information to his friends on Discord at the same time. So, really, an astonishing number of times when superiors could have intervened and failed to. An Air Force Inspector General’s report released this week was just excoriating on this front and said, essentially, that had his superiors done their jobs and reported him to security officials, they potentially could have stopped these leaks by several months.