JOHN YANG: Proponents of social media say that it bridges physical distance to build communities of like-minded people.

But what binds them together can sometimes be hatred and violence.

A joint investigation by ProPublica and PBS FRONTLINE details the shadowy world of online hate networks.

Their investigation focuses on the platform Telegram, and it's detailed in a new documentary, "The Rise and Fall of Terrorgram."

A.C. THOMPSON, Investigative Reporter, ProPublica: At first it's just a handful of chat rooms and channels on Telegram.

Then it is bigger and bigger, and finally it takes on a formal shape, and people within that group say, now we're starting something called the Terragram Collective, and this is going to be our organized arm that is going to generate in depth propaganda, in depth material for this community.

JOHN YANG: The investigation identified 35 crimes linked to Terrorgram, including bomb plots, stabbings, and shootings.

A.C. Thompson, who you just saw there, is one of the reporters who worked on the project.

He covers hate crimes and racial extremism for ProPublica and PBS Frontline.

A.C. for people who aren't familiar with Telegram, what is it about this platform that makes it so attractive to the people who form Terrorgram?

A.C. THOMPSON: Terrrogram is a massive, massive platform.

About a billion people use it, most of them outside of the US.

What was appealing to various types of extremists about Telegram was the fact that there was very little moderation on it.

So for a very long time, extremists of all different types, including the Terror Graham community, which was a white supremacist neo Nazi terror group, were able to use this platform to basically commit crimes.

JOHN YANG: One of the cases you look at in the documentary is the case of Yuri Krajczyk.

He's a teenager who carried out a shooting outside of a LGBTQ bar in Bratislava, Slovakia.

And you looked at his ties to Telegram, his ties to various people on Telegram.

Let's take a look at that.

PIERRE VAUX, Open source investigator: You're looking for what nodes turn up in networks over and over again.

So Krychick's account is Bob Bowie, and we can expand that one.

He was a very active user on these channels.

I've got another 40 channels he was in.

A.C. THOMPSON: Holy.

These are all chats?

PIRRE VAUX: Yep.

A.C. THOMPSON: Oh, wow.

JOHN YANG: What does his case tell us about these online hate networks?

A.C. THOMPSON: He's emblematic of the problems that we see here.

So he gets into the Telegram community when he's 16 years old, and over the span of three years, he is encouraged and groomed and pushed to engage in white supremacist terrorism.

And then finally, in 2022, he goes out and does it, and he attacks an LGBTQ bar.

He shoots three people and kills two, and the community that he'd been interacting with celebrates him as a hero and a saint and someone to emulate.

Your documentary includes a statement from Telegram, they told you that calls for violence from any group were not tolerated on our platform.

That said, why was the Terrorgram Collective allowed to sort of be there for so long?

A.C. THOMPSON: Yeah, that's a thing that was pretty disturbing to us.

You know, we can trace the early days of terrogram to 2019, and it starts with a couple of accounts, and it grows into this big community with hundreds of accounts and thousands of followers over about a five year span.

And in that time period, we didn't see real sustained efforts by Telegram to push these people off of the platform.

JOHN YANG: The defenders of these sites and the participants in these sites say they're merely using free speech, expressing free speech.

What do you make of that?

A.C. THOMPSON: The people that we're looking at in the telegram scene are not just saying, I'm racist, I'm antisemitic, I'm anti-LGBTQ.

What they were doing for five years, half a decade, was encouraging people to commit terrorist attacks.

So when went on to Telegram and investigated these spaces, we would find bomb making manuals, we would find poison recipes, we would find hacking tools, we would find hit lists.

It's just the sort of stuff that doesn't fall really into the free speech space, but falls into the terrorist material space.

This is about terrorism.

JOHN YANG: You mentioned earlier the sort of transient nature of these groups on these sites.

They move from one site to another.

What does that tell you about online hate groups?

A.C. THOMPSON: Over the last 10 years, I've been watching these groups and these actors move from one platform to the next.

And as they get bumped from one place because of hate speech, because of moderation, because maybe they're posting bomb materials, they go on to the next one.

And I think overall, the social media providers have not had a unified sort of strategy for dealing with this.

JOHN YANG: And from your reporting, what could deal with this?

Is it law enforcement?

Is it regulation?

A.C. THOMPSON: There's two pieces here.

I think what you really are looking at is good corporate behavior from the social media platforms, not allowing people to run a terrorist network on their site for years.

And they're just for a very long time, Telegram didn't seem to be responding to that kind of concern about criminal activity.

Now it has stepped up it's moderation.

It is policing the platform much more strongly these days than it did.

But it was a real wild thing to see that sort of material just circulating across a very large platform.

JOHN YANG: A.C. Thompson of ProPublica and PBS Frontline, thank you very much.

A.C. THOMPSON: Thank you.