Legal experts and court papers suggest that prosecutors will likely focus on whether Penny knew he was endangering Neely's life as he continued to squeeze the man's neck. Spodek said he expects the DA's office to question Penny's "minute by minute, second by second" decision-making process.

"They're going to try and tailor their theory of the case to the immediate circumstances. That what's happening in the larger New York City area is irrelevant," the attorney said. "The only thing that matters is what happened when they got on that train that very moment and nothing more."

Vinoo Varghese, a former Brooklyn prosecutor who now works in criminal defense, said he expects the DA's office to also highlight Penny's experience in the Marines.

"He kept holding onto this guy, and he's a trained military guy," Varghese said prosecutors will likely tell the jury. "He's not your ordinary citizen, and so he should have known that he was going to kill this guy."

Penny's defense attorneys, Spodek and Varghese both said, will likely focus more broadly on the day-to-day environment on New York City subways that could have influenced Penny's decision to put Neely in a chokehold.

In a motion to dismiss the case filed last year, Penny's attorneys described an atmosphere of "traumatizing" fear on the subway car after Neely boarded. They quoted passengers who said Neely's behavior was "insanely threatening" and "satanic," that he shouted "someone is going to die today" and that he was "ready to go to Rikers." They cited one long-time subway commuter's statement to the grand jury that she had encountered many things on the train, "but nothing that put fear in me like that."

Spodek said the jurors will have to ask themselves whether Penny reasonably believed that people on the F train were in danger.

"Was this unique? Was the circumstances to such a high level that he had no choice but to do this?" he said. "And I think the answer is, from the defense's point of view, absolutely. And there are witness observations to support that."

Varghese said he expects Penny's defense attorneys to try to pick jurors who can empathize with Penny and other riders who were scared on the subway that day. He said it could be more challenging to find those jurors in a largely Democratic borough.

"Amongst New Yorkers on this kind of political issue, in a city that leans overwhelmingly left and blue -- particularly in Manhattan -- it's going to be difficult for him," Varghese said.

"But," he added, "I think people are fed up with what they have to deal with on the subway."

Another central facet of the case is Neely's psychiatric history. He was diagnosed with schizophrenia and used synthetic cannabinoids -- also known as K-2 -- according to court records. Experts and court filings show that information is likely to come up at trial as defense attorneys try to convince jurors that Neely was scaring subway riders.

Neely's death fueled debates about the city's treatment of people with serious mental illness, particularly in the subway system. Mental health advocates told Gothamist they worry the trial will inflame rhetoric about subway crime and bolster misconceptions about mental illness and violence.

"It will perpetuate this stigmatization of people with mental illness," said Melissa Beck, who has worked as both a prosecutor and defense attorney and now advocates for mental health reform. "It will perpetuate the status quo of criminalizing people with mental illness, and it will do nothing to increase access to culturally competent, evidence-based care for people with mental illness."

On a recent evening at the Broadway-Lafayette station, lifelong New Yorker Nadya Belov said she's not sure what she would decide if she were a juror in Penny's case.

"I would have to really look at the evidence," she said, "because I wasn't there. I don't know what happened."

Belov said her first instinct is to help when she sees people in distress in the subway system, but she's often not sure how she can. And a lot of the time, she said, she feels scared.

"Sometimes people are screaming," she said. "I've seen a guy throw stuff. And then you're in the car as it's moving and someone is throwing something, and then at that point you no longer know what the person will do. So, you're like, 'What do I do?' Like, I don't want to be in the middle of this if something goes down."

Belov said when something like that happens, she normally switches cars at the next stop. So does Alve Al, a friend of Neely's who was sitting on a bench at the Broadway-Lafayette station last week. He said there was "no need" for Penny to choke Neely.

"I would have walked away," he said. "Life is more worth living. But for him to do what he did, he's going to have to pay the price."