Mass shooters don’t usually find yourself on trial. Many are killed or take their very own lives of their assaults, some forsaking a manifesto explaining why they acted, others leaving a thriller.

But in a trial that ended on Thursday with the imposition of a death sentence, scores of witnesses took turns dissecting the life and motivations of 1 middle-aged man who lived alone in a small residence earlier than finishing up the deadliest antisemitic assault in U.S. historical past: the killing of 11 worshipers in a Pittsburgh synagogue on Oct. 27, 2018.

From the testimony of outstanding psychiatrists and ageing relations emerged a portrait of the gunman, Robert Bowers, that was directly stunning and surprisingly acquainted. It depicted an remoted, sad man who had grown obsessive about darkish and deranged concepts, such because the notion that Jewish individuals had been a part of a conspiracy to destroy the white race.

“I see how the first time you hear it, it sounds pretty crazy,” Dr. Park Dietz, a forensic psychiatrist defined to the jury in testimony in early July. “But when you have seen this promoted for 20 years, 40 years, among thousands and thousands of people, in their books and the propaganda and online forums, it’s clear that these are subcultural beliefs.”

The protection legal professionals, argued that Mr. Bowers’s troubled childhood and psychological sicknesses had fueled weird, apocalyptic delusions. But Dr. Dietz and different consultants who testified for the prosecution mentioned that the protection “simply mistook very ordinary widespread white separatist beliefs for delusions because they weren’t familiar with them.”

If the federal government’s argument finally satisfied the jury, and introduced some measure of aid to the individuals who sat in courtroom just some steps away from the person who killed their family members, it was an argument that consultants say ought to give little consolation to anybody else.

In the net far-right fever swamps which have grown immensely because the synagogue bloodbath, the views Mr. Bowers expressed on social media 5 years in the past can be “simply unremarkable,” mentioned Oren Segal, the vp of the Anti-Defamation League’s Center on Extremism.

“There are thousands upon thousands upon thousands of people saying that stuff and even worse,” Mr. Segal mentioned.

Other consultants in risk evaluation agreed that there was little or no about what Mr. Bowers appeared to imagine that was distinctive.

The concept of the “great replacement” — that elites, and infrequently particularly Jewish individuals, are bringing in darker-skinned immigrants to “replace” white Americans — has been echoed by other purveyors of violence however can also be expressed routinely on right-wing web sites. A extra muted model of the “great replacement” idea was standard fare on Tucker Carlson’s show on Fox, which drew thousands and thousands of viewers each evening, and has even been espoused by members of Congress.

Andrew Torba, the chief govt of Gab.com, a far-right social media platform the place Mr. Bowers wrote and shared a whole bunch of virulently antisemitic posts, testified on the trial that there have been about 800,000 accounts on the positioning in 2018. In a 2022 company submitting, Gab reported having practically six million accounts, although it was unclear what number of had been lively.

“Technology has advanced in the last five years, and so there’s more ways of creating engagement over hatred of Jews or other communities,” Mr. Segal mentioned.

There are actually instruction manuals on-line for white supremacist would-be terrorists, he mentioned, and propaganda movies telegraphing bigoted harassment and even violence to the widest attainable viewers, an avenue for self-promotion far past Mr. Bowers’s terse put up on Gab earlier than the taking pictures. Mr. Segal identified that the 19-year-old white man who shot and killed 10 Black individuals at a grocery retailer in Buffalo in 2022 — who had carved Robert Bowers’s title onto his gun — livestreamed the bloodbath.

In a web-based sea of hateful and violent rhetoric, it has grow to be ever tougher to identify the true threats. There are sure alerts that risk evaluation consultants search for, mentioned Molly Amman, a former F.B.I. profiler who’s finding out the Bowers case. These embrace, she mentioned, a radicalized view of the hazard posed by some group of outsiders, and “a sense that something is fundamentally changing,” that “what I’m doing is no longer enough.”

The psychiatrists and different consultants who interviewed Mr. Bowers mentioned of their testimony that he expressed this type of visceral urgency to behave, seeing it as an obligation to guard his tradition from invasion. But he mentioned as a lot brazenly on Gab. Statements like this are all around the web, and the notion that civilization is being pushed to the sting of collapse has grow to be a standard trope of political and media rhetoric on the far proper.

There is a mixture of various components that improve the possibilities somebody will grow to be a harmful danger, mentioned Robert Pape, the director of the University of Chicago Project on Security and Threats. It is a sample obvious in different latest circumstances of violence — such because the mass shooting in El Paso in 2019 and the attack on Paul Pelosi final 12 months — and it was current in Mr. Bowers’s case as nicely.

He was an already unstable man, maybe affected by lifelong psychological problems. After the demise of his grandfather and his one shut buddy, he was remoted and alone. He spent his days on-line, immersed in conspiracy, what Mr. Pape referred to as “self-brainwashing.” And he turned satisfied that there was a risk manifesting, a “great replacement,” and that it was his responsibility to behave.

Some of the components that converged in his case are solely intensifying nationwide. Extremist content material continues to mushroom on-line, whereas the U.S. Surgeon General has warned of “an epidemic of loneliness and isolation.” Men particularly have grown more socially detached.

Mr. Pape mentioned it was too simplistic to declare that the expansion of those traits means there can be extra horrific tragedies.

But, he added, “we should prepare as if there will be more.”

Jon Moss contributed reporting.