The man who choked Jordan Neely to death on a New York City subway train on Monday is Daniel Penny, a 24-year-old veteran of the Marine Corps.

Mr. Penny has not been charged in Mr. Neely’s death and it is unclear if he will be. Many politicians, city leaders and advocates for New Yorkers struggling with homelessness and mental illness have called for his arrest. Mr. Neely’s death, they said, was an unnecessary tragedy that underscores the city’s inadequate policies toward its most vulnerable and marginalized residents. Some New Yorkers have also said that Mr. Penny’s actions reflect the frustration and fear many riders have about the transit system, even as the rate of major felony crimes on the subway has fallen.

On Friday evening, lawyers for Mr. Penny expressed condolences on behalf of their client to Mr. Neely’s family. “Daniel never intended to harm Mr. Neely and could not have foreseen his untimely death,” the law firm of Raiser and Kenniff said in a statement.

The firm said, “When Mr. Neely began aggressively threatening Daniel Penny and the other passengers, Daniel, with the help of others, acted to protect themselves, until help arrived.”

Lennon Edwards, a lawyer for the family of Mr. Neely, said in an interview on Friday that Mr. Neely’s death was unacceptable. “He was robbed of his life in a brutal way by someone who decided that they were judge, jury and executioner on the spot,” he said. “We can’t have vigilantes, and we can’t have people taking the law into their own hands.”

Mayor Eric Adams called Mr. Neely’s death “tragic,” but urged patience as officials completed the investigation. “There’s a lot we don’t know about what happened here,” he said earlier this week.

This is what we know so far about the case.

The police said they received a call at 2:27 p.m. on Monday about a fight on an F train at the Broadway-Lafayette Street subway station in Manhattan.

Shortly before that, Mr. Neely had boarded the northbound train at the 2nd Avenue station, said Juan Alberto Vazquez, a freelance journalist who recorded a nearly four-minute video that captured the moments when Mr. Penny was holding Mr. Neely in a chokehold.

Mr. Neely immediately began screaming, causing people who were sitting near him to move away, Mr. Vazquez recalled. Mr. Neely said he was hungry and thirsty and took off his jacket, throwing it down on the ground.

“‘I’m tired already,’” he said, according to Mr. Vazquez. “‘I don’t care if I go to jail and get locked up. I’m ready to die.’”

It is unclear if Mr. Penny said anything to Mr. Neely at that point. Mr. Vazquez said he did not see him grab Mr. Neely, but that he heard a thump and then saw both men on the floor. The train stopped at Broadway-Lafayette, where it remained standing while Mr. Neely was pinned down, as two other men grabbed his arms and legs.

At 2:29 p.m., another passenger can be heard in the video saying that his wife had been in the military and knew about chokeholds, and warning the men that they should make sure Mr. Neely had not defecated on himself.

“You don’t want to catch a murder charge,” he said. “You got a hell of a chokehold, man.”

The men then placed Mr. Neely, who was motionless, on his side. A transit worker can be heard over the loudspeaker calling for the police.

“He’s all right,” the passenger who had given the warnings said. “He ain’t gonna die.”

The police have not responded to messages asking what time they arrived at the scene. The Fire Department said it received a call for help at 2:39 p.m. and arrived at 2:46.

Mr. Neely was taken to Lenox Health hospital in Greenwich Village, where he was pronounced dead, the police said.

The medical examiner’s office said on Wednesday that the cause of death was compression of the neck, and ruled Mr. Neely’s death a homicide.

Mr. Neely was a dancer and artist known for his impersonation of Michael Jackson during his “Thriller” stage. He would dress up as the musician and ride the trains, moon-walking in front of commuters.

The subway was where he felt happy and free to perform as a dancer, his friends said.

But it was also clear that he was struggling. A friend, Moses Harper, recalled seeing him in 2016 walking through subway cars with his head down.

Ms. Harper said she gave him her shirt and some food and told him where she lived, urging him to come find her when he was ready to get help.

“He said, ‘I’m going to get it together,’” she said in an interview earlier this week. “And that’s the last time I saw him.”

At a protest over Mr. Neely’s killing on Thursday, demonstrators remembered seeing him perform. One man recalled being on a date once when his girlfriend stopped to watch Mr. Neely dance in Union Square.

“I’m a New Yorker: I know him,” said the man, Rashid Littlejohn. “I gave him money.”

John Rich, a subway performer, said he and Mr. Neely had danced together a few times.

“His glittery socks always matched his gloves,” Mr. Rich said, grinning at the memory. “He was serious about his outfit, serious about dancing.”

Mr. Penny is being represented by Raiser & Kenniff, a Manhattan law firm whose founding partners were both in the armed services.

He was interviewed by the police and released on Monday. A person familiar with the matter said Mr. Penny was not viewed by the authorities as a flight risk.

His lawyer, Thomas Kenniff, who was the Republican candidate for Manhattan district attorney in 2021, said that the firm had been in contact with the district attorney’s office and the Police Department about the incident.

In a news release about Mr. Neely’s killing on Thursday, the police asked for the public’s help in identifying witnesses they can interview. Prosecutors have also encouraged witnesses to come forward.

If Mr. Penny is charged by the Manhattan district attorney, Alvin L. Bragg, prosecutors would presumably have to prove that he used deadly force without having believed that Mr. Neely was also using deadly force or was about to. Mr. Edwards and his partner, Donte Mills, the lawyers for Mr. Neely’s family, said that witnesses had told them that Mr. Penny came up behind Mr. Neely and grabbed him.

The district attorney’s office said it was looking at a variety of factors before deciding whether to issue charges.

“As part of our rigorous ongoing investigation, we will review the medical examiner’s report, assess all available video and photo footage, identify and interview as many witnesses as possible and obtain additional medical records,” Doug Cohen, a spokesman for the office, said in a statement.

The investigation is being led by Joshua Steinglass, a veteran homicide prosecutor, the district attorney’s office confirmed. Mr. Steinglass helped lead the trial team in the case against Donald J. Trump’s family business.

Public defenders have said that law enforcement’s approach to filing charges in the case of Mr. Neely’s killing is atypical and that many people arrested in New York City are not afforded the same consideration.

“Police and prosecutors almost never apply the level of scrutiny to cases that they are extending in this instance,” said Eli Northrup, the policy director for the criminal defense practice at the Bronx Defenders. “The practice is to arrest and charge first, ask questions later, especially when the person being arrested is Black, brown or poor.”

There have been several protests in the wake of Mr. Neely’s death, including one at the Barclays Center in Brooklyn on Thursday night, when about 100 demonstrators walked down the street, blocking traffic, toward the 7th Precinct in Manhattan, where Mr. Penny was questioned on Monday.

“Man murders a man on the train. Chokes him to death,” Hawk Newsome, a founder of Black Lives Matter Greater New York, said to the crowd at Barclays.

“Police arrest him and decide, within hours, that they wouldn’t charge him,” Mr. Newsome said, adding, “They let him go.”

Wallace Mazon, 28, said the killing reminded him of George Floyd, who was killed when a police officer in Minneapolis put his knee on his neck and kept him pinned down for nearly nine minutes.

He cried when he saw the video of Mr. Neely dying.

“I kind of felt hopeless,” Mr. Mazon said. “I just wanted to be in community with other people and not feel so helpless.”

Other New Yorkers interviewed on the subway have expressed more ambiguous sentiments and even sympathy for Mr. Neely’s killer.

Maria Castaño, 64, an interior designer who lives in Brooklyn, said she viewed the man who choked Mr. Neely as a hero and Mr. Neely as the recipient of justice.

“I feel sorry for the man, but he was acting threatening,” she said.

Ayden James, 28, who is Black and a trans woman, said she knew what it was like not to feel safe on the subway.

“The train is always a scary place,” Ms. James said during Thursday’s demonstration. But she added that Mr. Neely did not seem threatening.

“He just was asking for help,” she said, “for food and for shelter.”

Jonah E. Bromwich contributed reporting. Susan C. Beachy contributed research.