The burgeoning online popularity of an alleged murderer, Luigi Mangione, could amount to more than mere online buzz — if it helps a jury acquit him of multiple counts of murder.

Mr. Mangione, who is a 26-year-old graduate of the University of Pennsylvania, is accused of slaying the chief executive of UnitedHealthCare, Brian Thompson. The killing took place at dawn on December 5, outside a hotel at Midtown Manhattan. In some quarters, Mr. Mangione is seen as something of an avenger against a healthcare system deemed predatory.

Mr. Mangione was later apprehended at Altoona, Pennsylvania, after surveillance footage from a hostel caught a partial image of his face. Appreciations of his appearance have proliferated online, and some have taken to garlanding him as a “folk hero” who struck a bloody blow against a rapacious industry. Some took to calling Mr. Mangione “the hot assassin.”

The support for Mr. Mangione appears to flow not only from his looks but also downstream from rage at the revenues reaped by the insurance agency and its procedures for determining coverage. UnitedHealthCare boasts totals in the hundreds of billions of dollars. One protester at Mr. Mangione’s arraignment held a sign that read: “Murder for Profit I$ Terrorism: Free Luigi.” Mr. Mangione’s manifesto gives further voice to these ideas.

One online defense fund for Mr. Mangione has raised nearly $200,000, and a poll conducted by Emerson College discloses that 41 percent of those in the 18-29 age range found Mr. Thompson’s killing “acceptable.” Support for his alleged crime has surged on TikTok, and the phrase “Deny, defend, depose,” words found on the bullet casings at the crime scene, has gone viral.

During Mr. Mangione’s arraignment at downtown New York last week, dozens of young women, many masked, lined up to voice their support for the accused, who faces both state and federal charges for murder. If he is convicted on the federal ones, the possibility of a death sentence looms. New York swore off capital punishment in 2004, but Mr. Mangione’s terrorism charge means he could spend life in prison without the possibility of parole. 

Mr. Mangione’s guilt or innocence, though, will be decided not by posters on Instagram or creators on X, but by a jury of his peers. The Sixth Amendment to the Constitution ordains that “in all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed.” That applies to state prosecutions as well. 

Mr. Mangione’s lawyer, Karen Friedman Agnifilo, ventured in court last week that she is “very concerned” about her client’s “right to a fair trial” because of comments made by Mayor Adams, who on PIX 11 explained why he was with the police escorting Mr. Mangione to court. The mayor said he I wanted to look Mr. Mangione “in the eye and state that, ‘You carried out this terrorist act in my city, the city that the people of New York love.’”  

Hizzoner’s press secretary, Kayla Mamolek, released a statement in response to Mrs. Agnifilo’s comments, declaring that the “cold-blooded assassination of Brian Thompson — a father of two — and the terror it infused on the streets of New York City for days has since been sickeningly glorified, shining a spotlight on the darkest corners of the internet.”

Before jurors in New York are dispatched to determine a verdict, the judge instructs them that “each of you must decide the case for yourself, but only after a fair and impartial consideration of the evidence with the other jurors.” The process by which jurors are selected is known as voir dire, which means “to speak the truth.” Attorneys for both sides probe potential jurors for bias. 

Each side is allowed a limited number of peremptory challenges, meaning they can strike a person without providing a reason, and an unlimited number of challenges for cause. The New York Bar Association explains that  “each juror must be fair and unbiased, able to render an impartial verdict in accord with the evidence and applicable law.”

New York courts explain that a “fair juror is a person who will keep the promise to be fair and impartial and will not base the decision in this case upon a bias or prejudice in favor of or against a person who may appear in this trial.” A fair juror must also be “mindful of any stereotypes or attitudes about people or about groups of people that the juror may have, and must not allow those stereotypes or attitudes to affect their decision.”

Mr. Mangione’s defense team is likely to be especially alert to any potential juror who has had negative encounters with insurance companies. One danger for the prosecution could be what is known as “jury nullification.” The Fully Informed Jury Association, which advocates for enthusiastic jury duty, explains that phenomenon as one where the jury “returns a not guilty verdict even though jurors believe beyond reasonable doubt that the defendant has broken the law.”

The Legal Information Institute reckons that “jury nullification is considered to be inconsistent with the jury’s duty to return a verdict based solely on the law and the facts of the case, and counsel is not permitted to present the concept of jury nullification to the jury.” Still, the practice boasts an American pedigree, traceable back to colonial juries refusing to enforce British law, resistance to the Fugitive Slave Clause, and opposition to Prohibition.

District Attorney Alvin Bragg has had a mixed recent record with respect to convicting high-profile defendants. His office persuaded a jury to bring in 34 “guilty” verdicts against President Trump, but a Marine, Daniel Penny, was acquitted of charges related to a violent altercation on the city’s subway. Famously, Lemrick Nelson Jr. was acquitted, despite overwhelming evidence, of killing Yankel Rosenbaum during the 1991 Crown Heights riots. He later confessed to the crime.