AMNA NAWAZ: On the day of the attack, the shooter wore an extremist insignia and left behind a social media trail of white supremacist beliefs.

Today, authorities confirmed his neo-Nazi affiliations, but they were cautious to say if he was targeting anyone specifically for their race, age or ethnicity when carrying out that attack in Allen, Texas.

He joins a growing list of individuals with far right extremist views who commit acts of mass gun violence.

Heidi Beirich is an expert on all of this, including the white supremacist movement.

She joins me now to discuss what she's uncovered about the gunman.

Heidi, welcome back to the "NewsHour."

You have been doing your own investigating into the gunman's background.

What does the evidence show you about what kinds of groups he was linked with?

What were his beliefs?

HEIDI BEIRICH, Global Project Against Hate and Extremism: Well, he was actually deep, deep into the world of white supremacy and neo-Nazism.

He was on Web sites like The Daily Stormer and VDARE that are connected with this.

He'd read a race war novel that inspired the Oklahoma City bombing.

And he left about 10 years' worth of diary entries that are absolutely filled with the worst hate you can imagine against Jews, Muslims, LGBTQ people, and others.

AMNA NAWAZ: Heidi, there was reporting he was wearing an RWDS patch on the day of the attack.

What does that mean?

What should we understand about?

HEIDI BEIRICH: Yes, RWDS stands for Right-Wing Death Squad, which is a reference to the Chilean dictator Pinochet's time in office, where he had death squads that killed communists, which he perceived as their -- as his enemies, and threw them out of helicopters.

And people in right-wing movements, like the white supremacist Proud Boys, wear these patches proudly and celebrate that errant way in history.

They like the idea of death squads.

And so this idea of RWDS has spread all throughout the Internet as a meme that you see in white supremacist and other extremist groups.

AMNA NAWAZ: Heidi, from what you have seen, do we have any idea when or how he began to be radicalized to hold these views?

HEIDI BEIRICH: Well, the diary entries actually go all the way back to when he was in high school, or at least he refers to being in ROTC.

And he talks about doing things like "Heil Hitler," salutes to Hitler, at that time and being criticized by a teacher.

He talks again about his very short stint in the Army, before they threw him out, and meeting white supremacists and becoming a white supremacist at that time.

So this has been a long process going back to at least 2008 or 2009.

AMNA NAWAZ: Authorities have identified the gunman as a 33-year-old man named more Mauricio Garcia.

He is not white.

And it is confusing for many people how a person of color could hold white supremacist views.

What should we understand about that?

HEIDI BEIRICH: Well, he actually writes in his diary of appearing -- of a period of self-loathing, where he hated the fact that he was Hispanic.

And people should understand that their -- the attraction of white supremacy can cross race.

People want to be identified with what they consider, especially if they have been radicalized like this individual, the most powerful entities in society.

And he's not the only one.

Enrique Tarrio, the head of the Proud Boys, who was just convicted for seditious conspiracy related to January 6, is an Afro-Cuban.

And there are other examples.

And so it's very naive to think that somebody can't choose to have a different ethnicity, to identify as white and be involved in these movements just because they were born of a different ethnicity.

And people should try to - - should understand that.

AMNA NAWAZ: Allen, Texas, is a very diverse area.

Collin County, where the town is, is home to Texas' largest and fastest growing population of minority groups.

And Asian Americans were among the majority of those killed.

There were Latinas and Latinos as well.

Would someone who holds these kinds of views and has a proclivity for violence, would they target an area like this?

HEIDI BEIRICH: Yes, we don't know exactly what the motive of this individual was.

But it is possible, given this history of white supremacy and deep hatred for so many minority populations, that he may have chosen the mall for that reason.

That isn't evident in his writings, but he does scope out the mall and lay out the plans for his attack in those writings.

We just don't know what the exact motive is.

AMNA NAWAZ: Heidi, we report often about the connection between online hateful rhetoric and real-world violence.

Do we have any knowledge, any statistics about how frequently these kinds of mass attacks or mass shootings are carried out by people who hold these far right extremist views?

Do we know that?

HEIDI BEIRICH: Well, we have had several major attacks, for example, at the Tree of Life Synagogue in Pittsburgh, the El Paso Walmart shooting from a few years ago, last year the shooting at a Buffalo supermarket that targeted Black people, where the individuals involved were radicalized online.

And they all believed something that this shooter also believed, that there's some kind of a Great Replacement going on, white people being displaced by people of color and immigrants.

It's often viewed as something driven by Jews or globalists.

So the online space is probably what is the biggest factor in causing people to be radicalized into violence.

AMNA NAWAZ: Heidi Beirich, we thank you so much for joining us tonight, helping us to understand this a little bit better.

Thank you for your time.

HEIDI BEIRICH: Thank you.