The killing of a 30-year-old homeless Black man by a white rider on a New York City subway car has prompted intense debate over the response by the police and prosecutors.

Ten days after the May 1 killing, Alvin L. Bragg, the Manhattan district attorney, filed a felony complaint of second-degree manslaughter against Daniel Penny, the 24-year-old ex-Marine who choked Jordan Neely to death on the F train in a killing that was captured on a four-minute video.

Questions remain about why prosecutors waited and whether public outrage might have affected their choices.

“All of that public scrutiny on the one hand is a motivation for acting quickly, but on the other hand, it raises the stakes of being very thorough,” said Brandon del Pozo, a former New York City police commander, who is now a researcher at Brown University.

“Whatever happens will be very highly scrutinized,” he said.

What decisions did the Manhattan district attorney’s office have to make?

Arrest immediately or indict?

Mr. Penny was questioned by the police and released on the day Mr. Neely died, a decision that drew condemnation from many political leaders on the left and protesters.

He could have been arrested that night if the police found probable cause to bring assault or even homicide charges, legal specialists said.

Witnesses said that Mr. Neely was behaving in a “hostile and erratic manner,” according to the police. Juan Alberto Vazquez, a journalist who filmed the choking, said that after Mr. Neely boarded the F train at the Second Avenue station, he began yelling that he was thirsty, hungry and “ready to die.” Prosecutors said Mr. Neely was “making threats and scaring passengers” when Mr. Penny came up from behind and placed him in a chokehold.

The police arrived within six minutes of a 911 call, but several witnesses, including Mr. Vazquez, had left before they arrived. The medical examiner’s office did not rule on a cause of death until two days later. Mr. Penny was not considered a flight risk or a danger to the public.

The evidence to charge Mr. Penny with a homicide before the medical examiner’s ruling was not strong. “A fast arrest would have been a foolish decision,” said Howard Tanner, a Manhattan defense attorney.

Mr. Penny’s lawyers have indicated that they plan to argue he was acting to defend himself and others. To get a conviction, prosecutors will have to prove that Mr. Penny used deadly force without having reasonably believed that Mr. Neely was also using deadly force or was about to.

That requires interviewing as many witnesses as possible to ensure that none would help Mr. Penny argue that force was justified. By waiting to bring a felony complaint, prosecutors gave investigators time to find and interview people who would bolster the case.

Filing a felony complaint also helped prosecutors avoid the longer, less predictable process of letting a grand jury decide whether to charge Mr. Penny, said Todd Spodek, a defense attorney in Manhattan.

Before the case can go to trial, a grand jury still must vote to indict Mr. Penny.

Prosecutors could have gone to the grand jury first, but Mr. Spodek said that filing a felony complaint allowed Mr. Bragg to do two things: bring charges more quickly and rebuff public accusations that law enforcement did not care about Mr. Neely’s death.

“He can say, ‘I’ve done my part, I’ve investigated and I believe there is probable cause for an arrest,’” Mr. Spodek said.

Grand juries generally hand up indictments that prosecutors are seeking, but there are cases where grand jurors accept a justification of self-defense. If the grand jury ultimately votes not to indict Mr. Penny, Mr. Bragg can tell the public it was not because prosecutors failed to take the case seriously.

“It does give him a little cushion,” Mr. Spodek said.

Does public opinion affect prosecutors?

The longer prosecutors take, the more inflamed a community can become, said Kami Chavis, a former federal prosecutor who is a professor at William & Mary Law School.

But rushing an investigation to mollify the public can jeopardize a case, she said.

“It’s really important that the D.A.’s office conduct a thorough investigation in order to honor the victim,” Ms. Chavis said.

The prosecutor handling Mr. Penny’s case is Joshua Steinglass, a longtime assistant district attorney who also led the prosecution of the Trump Organization.

“The public pressure is irrelevant to him. He could care less,” said Karen Friedman Agnifilo, a former prosecutor who supervised Mr. Steinglass when she worked at the Manhattan district attorney’s office.

“The fact that he agreed to charge him makes me feel that there was not pressure” to prosecute Mr. Penny, she said. “Josh would push back on that.”

Still, it is unrealistic to think that Mr. Bragg did not consider public opinion, said William J. Bratton, a former New York City police commissioner. “The city was in turmoil night after night,” he said.

Minimizing that anger and defusing tensions are legitimate considerations in the timing of an arrest, Mr. Bratton said.

“It should not be the sole determinant of what you’re going to do,” he said. “Is it a factor? Definitely. You have a responsibility as the district attorney, mayor and the police to keep the public safe. Public safety has to be the ultimate concern.”

Why manslaughter charges?

Prosecutors are likely to have weighed three charges against Mr. Penny: manslaughter in the first degree, manslaughter in the second degree and criminally negligent homicide, legal specialists said.

Manslaughter in the first, which carries a maximum sentence of 25 years, would require proving Mr. Penny intended to hurt or even kill Mr. Neely, a high hurdle, Mr. Spodek said.

Criminally negligent homicide has a much lower standard: Prosecutors would have had to show that a defendant acted negligently enough to lead to a death. That charge carries only a four-year maximum sentence.

To prove manslaughter in the second degree, which carries a 15-year maximum sentence, prosecutors must prove that Mr. Penny’s behavior was not only reckless, but that he was aware his actions could kill Mr. Neely.

Marines are trained on how to use chokeholds. His military background could help prosecutors show he should have been aware he could kill Mr. Neely.

Mr. Penny, however, could make a compelling case to grand jurors who ride the subway and fear for their safety, Ms. Friedman Agnifilo said.

“If I were his lawyer,” she said, “I would counsel him to testify before the grand jury because I think he has a perspective that could be sympathetic.”