At about 6 a.m. on Thursday, nearly a dozen men and women dressed in business attire arrived in S.U.V.s outside the entrance of Gracie Mansion, the mayor’s official residence, on the Upper East Side. At least one vehicle had a federal law enforcement parking placard on its dashboard. They carried briefcases, backpacks and bags.

A lawyer for Mr. Adams, Alex Spiro, issued a statement on Thursday saying that the agents had come for the mayor’s phone, even though investigators had taken some electronic devices from him last year.

In a statement sent by email, Mr. Spiro said: “Federal agents appeared this morning at Gracie Mansion in an effort to create a spectacle (again) and take Mayor Adams phone (again). He has not been arrested and looks forward to his day in court. They send a dozen agents to pick up a phone when we would have happily turned it in.”

The indictment remained sealed on Thursday morning, and it was unclear what specific charge or charges Mr. Adams, a Democrat, would face. It was also unclear when he would surrender to the authorities.

On Wednesday night, a number of elected officials called for him to resign, including several Democrats running against Mr. Adams in next year’s Democratic primary. Gov. Kathy Hochul has the power to remove him from office; she has yet to comment on the indictment.

But Mr. Adams proclaimed his innocence. “I always knew that if I stood my ground for New Yorkers, that I would be a target — and a target I became,” Mr. Adams, 64, said in a taped video.

Mr. Adams, a retired police captain, was elected New York’s 110th mayor in 2021 after a campaign built on a pledge to reduce crime and bring professionalism to City Hall. His inner circle has been engulfed by federal investigations that have targeted the highest officials in city government, some of whom have recently resigned.

Here’s what else to know:

What could happen: If Mr. Adams resigns, the acting mayor would be Jumaane Williams, New York City’s public advocate. He would schedule a nonpartisan special election for a new mayor, which could take place within 90 days. Read more about potential next steps.

Timeline: The investigation involving Mr. Adams burst into public view nearly a year ago when the F.B.I. raided the home of his chief fund-raiser. Investigators seized his electronic devices a few days later. Read more about key events leading up to the indictment.

Array of inquiries: Four federal investigations have ensnared the Adams administration and high-ranking officials, including the police commissioner and the schools chancellor. Read more about the investigations.

Mr. Williams has been slowly working behind the scenes to prepare for the job, and began talking with his allies about the scenario as early as last year, not long after the mayor’s cellphone and other electronic devices were seized in November, according to two people familiar with the matter.

More discussions have taken place this month in the wake of the abrupt resignation of Lisa Zornberg, the mayor’s chief legal counsel. Mr. Williams has also spoken with his staff, including the public advocate’s counsel, about how a transition might proceed, according to a person familiar with the matter.

Mr. Williams told reporters recently that he doubted the mayor’s ability to navigate the federal investigations, and that he was ready to take over if necessary.

“That’s part of the job,” he said. “Is it something that you want to happen? No.”

As news of the mayor’s indictment circulated, the list of Democrats calling for his resignation grew to include at least three of Mr. Adams’s primary challengers and the Working Families Party, a prominent progressive group.

Mr. Williams, however, did not call for the mayor to step down. His office released a statement saying the indictment was “incredibly serious.”

“As the facts emerge, the public advocate will have more to say to the people of New York City, and right now, he is focused on how best to ensure that New Yorkers can regain trust, confidence and stability in city government,” the statement said.

If Mr. Williams were to become mayor, his agenda would be a stark departure from the tenure of Mr. Adams, a moderate Democrat with a law enforcement background and a pro-business agenda.

Mr. Williams, a staunchly progressive Democrat, built a reputation for speaking out against discriminatory practices and getting arrested to protest them. He has become a fierce critic of Mr. Adams, especially over the city’s increasing reliance on stop-and-frisk policing tactics.

His potential ascension would set the stage for a special election that could draw the four Democrats who have already entered next year’s mayoral race, as well as a formidable undeclared candidate: former Gov. Andrew M. Cuomo. Mr. Williams would likely run in the election, which could take place by the end of the year.

The four candidates currently competing against Mr. Adams are Brad Lander, the city comptroller; Scott Stringer, a former comptroller; Zellnor Myrie, a state senator from Brooklyn; and Jessica Ramos, a state senator from Queens. All of them are politically to the left of the mayor and Mr. Cuomo, who resigned in 2021 over a sexual harassment scandal.

Mr. Cuomo has been trying to make a return to politics, and is considering running for mayor. Mr. Cuomo would likely prefer to run in a special election with a truncated timeline, where he could rely on name recognition and avoid months of additional scrutiny.

Over the last week, the candidates and would-be candidates have sought to portray themselves as alternatives to Mr. Adams. Mr. Lander met with business leaders at a breakfast in Manhattan, where he cast himself as a responsible fiscal manager and pledged to end street homelessness of severely mentally ill people.

Mr. Cuomo, who has been grappling with the fallout over his response to the pandemic, spoke on Sunday at Bedford Central Presbyterian Church in Brooklyn and portrayed the city as out of control.

Without naming Mr. Adams, Mr. Cuomo said that political leaders were “all talk but no action,” adding that “government is supposed to build, accomplish, improve your life.”

Former Gov. David Paterson told City and State that Mr. Cuomo joked to him recently that he would prefer to run for governor, but that he would settle for mayor.

Mr. Paterson said in an interview that a matchup between Mr. Williams and Mr. Cuomo would be interesting, and that Mr. Williams was “not someone to take lightly.”

“He’s a very smart person — he’s very likable and very thoughtful,” he said.

Mr. Williams, 48, a former City Council member, was elected public advocate in 2019. He ran unsuccessfully for lieutenant governor the year before and for governor in 2022.

He has spoken candidly over the years about seeking therapy for mental health challenges, his family’s fertility challenges and living with Tourette’s Syndrome.

When Mr. Adams took office in January 2022, Mr. Williams tried to find common ground with him on issues such as gun violence, and was measured in his criticism. But their relationship soured earlier this year over the How Many Stops Act, which required the police to record more information about the people they question in the hopes of reducing illegal stops.

Mr. Adams vetoed the legislation, which Mr. Williams had sponsored. The City Council overrode the mayor’s veto.

“The thing about Jumaane that is different and really distinguishes him from Eric Adams and other people in the city is that he is a trusted leader,” said Jasmine Gripper, a co-director of the left-leaning Working Families Party. “He will lead from a place that is deeply rooted in helping the most marginalized communities.”

Mr. Williams would be the first public advocate, a position created in 1993, to become acting mayor. If that were to happen, he would set a date for a special election to pick a mayor, likely within the next three months, according to the City Charter. The earliest it would happen would be late November.

The thought of Mr. Williams becoming mayor, even temporarily, has raised concerns among some business and real estate leaders who object to his progressive background.

“It’s a prospect I don’t want to consider,” said Bruce Teitelbaum, a real estate developer who recently expressed support for Mr. Adams in an ad in the Flatbush Jewish Journal.

As of now, Mr. Adams has made it clear that he intends to stay in office and contest the charges, saying in a video that he would “fight this with every ounce of my strength and spirit.”

If Mr. Adams remains in office, Gov. Kathy Hochul has the power to remove him. But the pair have been aligned on many issues, and she has been generally supportive of the mayor during the course of the investigations.

At the mayor’s town hall meeting on Monday, Maria Forbes, the leader of a tenant group in the Bronx, said that after navigating the criminal justice system for her own son, who is in prison, she believed in due process for Mr. Adams.

She had mixed feelings about Mr. Williams, but her face lit up at the prospect of voting for Mr. Cuomo: “That’s my friend.”

“I think that he would be able to run and operate the city,” she said.

It’s one of several federal corruption investigations that have ensnared Mr. Adams’s administration. Here are some key events that led up to the indictment of the mayor:

Nov. 2, 2023: The F.B.I. raids the home of the chief fund-raiser to Mayor Eric Adams.

Federal agents raided the Brooklyn home of Brianna Suggs, a recent college graduate who had been in charge of Mr. Adams’s fund-raising operation when he ran for mayor in 2021. Ms. Suggs was 23 years old when the mayor picked her for the job, and many Democratic officials who worked in fund-raising were shocked that he had chosen someone for the role with so little professional experience.

The agents seized three iPhones and two laptop computers from Ms. Suggs’s home; they also took papers and other evidence, including something agents identified as a “manila folder labeled Eric Adams,” as well as seven “contribution card binders” and other materials, according to the search warrant documents.

Nov. 2, 2023: The F.B.I. raids the homes of an aide in the mayor’s international affairs office and a former Turkish Airlines executive who served on his transition team.

Investigators also searched the New Jersey homes of Rana Abbasova, an aide in Mr. Adams’s international affairs office, and Cenk Öcal, a former Turkish Airlines executive who served on his transition team, according to people familiar with the matter.

Ms. Abbasova was the mayor’s longtime liaison to the Turkish community when Mr. Adams was Brooklyn borough president. Mr. Öcal was the general manager of the New York office of Turkish Airlines until early 2022.

Nov. 6, 2023: The F.B.I. seizes the mayor’s phones and iPad.

In early November, F.B.I. agents approached Mr. Adams and his security detail after he had attended an event in Manhattan. The agents asked the security team to step aside before climbing into the mayor’s S.U.V. with him and taking his devices, pursuant to a court-authorized warrant. The devices were returned to the mayor within a matter of days, according to two people familiar with the situation. Law enforcement investigators can make copies of data on seized devices.

A lawyer for the mayor, Boyd Johnson, said at the time that Mr. Adams had not been accused of wrongdoing and had “immediately complied with the F.B.I.’s request and provided them with electronic devices.”

Mr. Johnson also said that Mr. Adams had already “proactively reported” at least one instance of improper behavior.

Nov. 28, 2023: Adams announces that his chief fund-raiser is out.

Weeks after agents searched Ms. Suggs’s home, Mayor Adams said during a weekly press briefing that she was no longer managing his political fund-raising. He declined to say why he had removed her from the position. Ms. Abbasova was also placed on leave after City Hall learned she had “acted improperly,” according to a spokesman for the mayor.

Feb. 5, 2024: A retired police inspector pleads guilty to funneling illegal funds to the mayor’s campaign.

Dwayne Montgomery, a former police inspector, pleaded guilty to misdemeanor conspiracy, admitting to directing straw donors — people who make campaign contributions using someone else’s money — to contribute to the mayor’s campaign. Mr. Montgomery was indicted in July 2023, along with four construction executives and a bookkeeper. Mr. Montgomery agreed in his plea not to organize or host any fund-raisers or to solicit contributions for a campaign, for one year.

The mayor was not implicated in the indictment nor accused of any wrongdoing.

Feb. 29, 2024: The F.B.I. searches the homes of the mayor’s Asian affairs adviser, who was a prominent fund-raiser for his campaign.

Agents searched two houses that belonged to Winnie Greco, an aide who was a prominent fund-raiser and who had close ties to the Chinese community in New York City. She became the mayor’s director of Asian affairs when he took office in 2022. The searches were part of an investigation conducted by prosecutors from the U.S. attorney’s office in Brooklyn and it was unclear what the investigation was focused on and whether it was related to the mayor.

Agents also executed a search warrant at the New World Mall in Flushing, Queens, where Mr. Adams had made regular appearances, including to deliver remarks at a Lunar New Year gala.

July 2024: Federal prosecutors serve a new round of subpoenas to the mayor, his election committee and City Hall.

The subpoenas sought information in a number of areas, including travel by the mayor, his aides and others, and fund-raising. It was unclear what prompted the new subpoenas.

Sept. 4, 2024: Federal agents seize the phones of the police commissioner, the first deputy mayor, the schools chancellor and others.

Top city officials who had their phones seized included the police commissioner, Edward A. Caban; the first deputy mayor, Sheena Wright; her partner, David C. Banks, the schools chancellor; the deputy mayor for public safety, Philip Banks III; and a senior adviser to the mayor, Timothy Pearson.

The seizures appeared to be separate from the corruption investigation focused on the mayor and his campaign fund-raising, but the actions further destabilized his administration.

Terence Banks, a consultant who is the brother of both the schools chancellor and the deputy mayor of public safety, had his home searched and his phone seized. Agents seized the phones of his brothers because they believed they might find evidence of bribery and other crimes, including fraud and violations of the Travel Act, according to people with knowledge of the matter.

Sept. 12, 2024: The police commissioner resigns.

Mr. Caban, the New York police commissioner, resigned at the request of City Hall, which asked him to step aside after federal investigators seized his phone. Media coverage about the investigations had “created a distraction for the department,” Mr. Caban said in an email to members of the Police Department.

Lawyers for Mr. Caban said in a statement that federal prosecutors had told them that he was not a target of the investigation and that he intended to fully cooperate with the government.

Sept. 15, 2024: The mayor’s chief counsel resigns.

Lisa Zornberg resigned from her post as the mayor’s counsel and chief legal adviser. She had been one of the mayor’s fiercest defenders, encouraging New Yorkers not to rush to judgment. She formerly worked as a senior Manhattan federal prosecutor in the office that is currently conducting three separate corruption investigations into the mayor and some of his senior aides.

Sept. 16, 2024: Two former Fire Department chiefs are arrested on bribery charges.

Brian E. Cordasco, 49, and Anthony M. Saccavino, 59, ran the Department’s Bureau of Fire Prevention until earlier this year. They were arrested and accused of accepting tens of thousands of dollars in bribes to speed up the fire-safety approval process for building projects across the city.

There was no indication that the case is related to any of the federal corruption investigations swirling around the mayor, his campaign and some of his most senior aides.

Sept. 21, 2024: Federal agents search the home of the interim police commissioner.

Thomas G. Donlon, who took the interim role after Mr. Caban resigned, said federal agents searched his home and seized materials that were unrelated to the Police Department. According to two federal officials with knowledge of the matter, the materials were classified documents that had been in Mr. Donlon’s possession for years.

Sept. 23, 2024: The city’s health commissioner says he will resign.

Dr. Ashwin Vasan, who led New York City out of the coronavirus pandemic, became the third top administration official to resign in September amid the investigations. His decision will go into effect early next year. Dr. Vasan said he decided to step down because he wanted to spend more time with his family. A City Hall spokesman said the departure was unrelated to the federal inquiries, and the commissioner affirmed that in a brief interview with The Times.

Sept. 23, 2024: It is reported for the first time that federal prosecutors are looking into the mayor’s dealings with five countries besides Turkey.

The other countries are Israel, China, Qatar, South Korea and Uzbekistan and the demand for information was made in expansive grand jury subpoenas issued in July to City Hall, the mayor and his campaign. This information had not been previously reported.

Sept. 24, 2024: The schools chancellor says he will resign.

David C. Banks, the chancellor of the New York City public schools system, said that he would resign from his role at the end of December. The announcement came weeks after federal agents seized his phone.

Sept. 25, 2024: Representative Alexandria Ocasio-Cortez becomes the most prominent elected official to call for Adams’s resignation.

Ms. Ocasio-Cortez, who represents parts of Queens and the Bronx, said in a statement to The New York Times that she could “not see how Mayor Adams can continue governing New York City.”

“The flood of resignations and vacancies are threatening government function,” she said. “Nonstop investigations will make it impossible to recruit and retain a qualified administration.”

“For the good of the city,” she added, “he should resign.”

The call from Ms. Ocasio-Cortez, a national leader of the Democratic Party’s progressive wing, came after a handful of other New York lawmakers urged Mr. Adams to step down.

Sept. 25, 2024: News of Mayor Eric Adams’s indictment is made public.

Eric Adams will be the first sitting New York City mayor to face criminal charges.

When the indictment is made public, Mr. Adams, a Democrat, will become the first New York City mayor to face a federal charge while in office. It was not clear when he will surrender to the authorities. Federal prosecutors were expected to announce more details on Thursday.

The indictment promised to reverberate across the nation’s largest city and beyond, plunging Mr. Adams’s embattled administration further into chaos just months before he is set to face challengers in a hotly contested mayoral primary.

And, if it contains allegations of conspiring to commit crimes with foreign nationals, it will have landed on the same week that the city was playing host to leaders from across the world at the United Nations General Assembly, including Turkey’s president, Recep Tayyip Erdogan.

Mr. Adams struck a defiant tone in a video statement issued Wednesday, insisting that he had done nothing wrong.

“I always knew that if I stood my ground for New Yorkers that I would be a target — and a target I became,” he said. “If I am charged, I am innocent, and I will fight this with every ounce of my strength and spirit.”

Brendan R. McGuire, who with his partner at WilmerHale, Boyd M. Johnson III, represents the mayor, said the lawyers had no comment.

Representatives of the agencies that conducted the investigation into Mr. Adams — the U.S. attorney’s office for the Southern District of New York, the F.B.I. and the city’s Department of Investigation — declined to comment.

Even before he was indicted, Mr. Adams’s administration had been battered not just by the investigation into him and his campaign but by three separate inquiries involving some of his highest ranking aides and advisers — investigations that included a drumbeat of searches and seizures that destabilized City Hall and made it difficult for him to govern effectively.

Calls for Mr. Adams’s resignation had been steadily accumulating over the past several weeks.

Earlier on Wednesday, Representative Alexandria Ocasio-Cortez of New York said she could “not see how Mayor Adams can continue” in his job.

On Wednesday night, the news of the indictment fueled the criticism. Scott Stringer, the former New York City comptroller who is among the Democrats running against Mr. Adams in next year’s mayoral primary, said that the mayor was presiding over “a broken-down train wreck of a municipal government” and that he should step down.

The indictment represented an extraordinary turnabout for Mr. Adams, 64, a former state senator and Brooklyn borough president who took office as the city was rebounding from the pandemic and about to confront a massive influx of migrants from the southern border.

It grew out of an investigation by the F.B.I. and federal prosecutors in Manhattan that began in 2021 and was focused at least in part on the possible foreign donations, and on whether Mr. Adams pressured officials in the Fire Department to sign off on the opening of a new high-rise consulate building for the Turkish government despite safety concerns.

The investigators were also examining whether Mr. Adams accepted pricey flights and upgrades on Turkish Airlines, which is partly owned by the Turkish government. And they sought information about a Brooklyn construction company run by Turkish Americans, and a small university in Washington, D.C., with Turkish ties.

Mr. Adams has said he has visited Turkey at least six times and that he met Mr. Erdogan when Mr. Adams was Brooklyn borough president.

The inquiry remained secret until late last year, when an F.B.I. search of his chief fund-raiser’s home thrust it into public view. After searching the home of the fund-raiser, Brianna Suggs, last November, federal investigators left with two laptop computers, three iPhones and a manila folder labeled “Eric Adams.” Ms. Suggs has not been accused of wrongdoing.

Days later, in a dramatic scene on a Greenwich Village street, F.B.I. agents told the mayor’s security detail to step aside, climbed into his S.U.V. with him and seized his electronic devices.

On the day of the search at Ms. Suggs’s home, agents also searched the New Jersey homes of Rana Abbasova, the director of protocol in the Mayor’s Office for International Affairs and Mr. Adams’s former liaison to the Turkish community, and Cenk Öcal, a former Turkish Airlines executive and member of the mayor’s transition team. Neither Ms. Abbasova nor Mr. Öcal has been publicly accused of wrongdoing.

But the investigation into Mr. Adams has already affected the careers of Ms. Suggs and Ms. Abbasova. Ms. Suggs left her position as the mayor’s fund-raising chief, he said after her home was searched, and City Hall placed Ms. Abbasova on leave after discovering she had “acted improperly,” according to a spokesman for the mayor.

Weeks later, Ms. Abbasova turned against the mayor, and she has been cooperating with the investigation. Her lawyer, Rachel Maimin, a former federal corruption prosecutor who is a partner at Lowenstein Sandler, could not immediately be reached for comment.

Until federal investigators closed in on him, Mr. Adams’s life had seemed a classic New York success story.

Raised by a working-class mother in Brooklyn and Queens, he overcame dyslexia and run-ins with the police, and then joined the Police Department himself.

During his time with the department, he rose to lead two groups that represented Black officers, the Guardians Association and 100 Blacks in Law Enforcement Who Care.

In those roles, he often criticized police leaders for their policies and their treatment of Black officers, but nonetheless advanced to the rank of captain by passing promotional exams.

Mr. Adams was investigated by the department four times, including for associating with criminals, one of whom was the boxer Mike Tyson, who was convicted of rape. Mr. Adams has said he did nothing wrong and cast the scrutiny as retaliation for his activism.

His first foray into politics, a run for Congress at 33, did not go far. A decade later, in 2006, he won a State Senate seat, beginning a seven-year tenure that included three re-election victories.

In 2010, New York’s inspector general found that Mr. Adams and other Senate Democrats had fraternized with lobbyists and accepted significant campaign contributions from people affiliated with contenders for a video lottery contract at Aqueduct Racetrack. The findings were referred to federal prosecutors, but no charges were brought.

During his fourth Senate term in 2013, Mr. Adams successfully ran for Brooklyn borough president, an office he would use as a jumping-off point for his bid for City Hall. Early in his tenure in Brooklyn, he organized an event to raise money for a new nonprofit, One Brooklyn, which had yet to register with the state. The invitation list was based on donor rolls for nonprofits run by his predecessor, records show.

A city Department of Investigation inquiry concluded that Mr. Adams and One Brooklyn appeared to have solicited money improperly from groups that either had or would soon have matters pending before the borough president’s office.

Mr. Adams’s aides emphasized to investigators that the slip-ups had occurred early in his administration, and promised to comply with the law in the future.

For years during his political career, Mr. Adams dreamed of becoming New York’s mayor, an ambition he realized by embracing diverse constituencies across the city, and an accomplishment he has said was divinely ordained.

As mayor, Mr. Adams vowed to return “swagger” to a city still emerging from the pandemic, and he surrounded himself in City Hall with friends and associates whose loyalty to him sometimes exceeded their policy expertise. Several had troubled pasts.

But his 33-month tenure as mayor has been marred by more scandal. In July 2023, the Manhattan district attorney, Alvin L. Bragg, charged six people, including a retired police inspector who had worked and socialized with Mr. Adams, with conspiring to funnel illegal donations to the mayoral campaign.

Two months later, Mr. Bragg charged Eric Ulrich, the mayor’s former senior adviser and buildings commissioner, with conspiracy and taking bribes. Mr. Bragg accused Mr. Ulrich of using his city-funded position to “line his pockets.” Mr. Ulrich has pleaded not guilty.

More recently, federal agents seized the phones of some of the highest-ranking officials in city government, including the police commissioner, the schools chancellor, the first deputy mayor, the deputy mayor for public safety, and a senior adviser who has been sued four times this year for sexual harassment. Those searches and seizures were related to the separate federal criminal investigations that were being conducted in parallel to the inquiry involving Mr. Adams. None of those officials has been charged with a crime.

Although he will become the first sitting mayor to be criminally charged, Mr. Adams is hardly the first to face criminal investigation. Jimmy Walker, a flamboyant, nightlife-loving mayor known as Beau James, held court in Jazz Age New York City but resigned amid a corruption scandal and fled to Europe.

Mayor William O’Dwyer, the only modern mayor aside from Mr. Adams to have served as a police officer, resigned months into his second term amid what was described in his obituary as “the biggest police scandal in the city’s history.”

More recently, federal prosecutors investigated Bill de Blasio, Mr. Adams’s predecessor, over his interactions with donors, but brought no charges. And Rudolph W. Giuliani was indicted this year, more than two decades after he was mayor, in a Georgia case focused on efforts to overturn the results of the 2020 presidential election.

Susan C. Beachy contributed research.

Investigators are looking for evidence that would support bribery, fraud and conspiracy charges, said the person, who, lacking authorization to discuss the case publicly, asked to speak anonymously. No one in the Police Department has been arrested or charged.

The person’s account gave a fuller picture of what investigators have been seeking as they have fanned out through the city, issuing search warrants and subpoenas to members of Mayor Eric Adams’s administration, which has been engulfed in at least four federal inquiries that have already led to several resignations.

Edward Caban, 57, was the first to resign on Sept. 12, at the request of City Hall, which had asked him to step aside after federal agents seized his phone on Sept. 4 as part of a criminal investigation.

Mr. Caban, whose departure ended a career that spanned more than 30 years at the Police Department, said he was leaving because “the noise around recent developments” had made it impossible for him to lead the agency.

His lawyers have said he is not the investigation’s target.

“He expects to cooperate fully with the government,” his lawyers, Russell Capone and Rebekah Donaleski, said Wednesday.

Sean Hecker and David Patton, lawyers for James Caban, a former police officer who was fired from the department more than two decades ago, said that he “unequivocally denies any wrongdoing.”

Mr. Caban was fired after he detained and threatened a livery cabdriver whom he had accused of stealing money from his wife’s purse.

His lawyers described him as a consultant who serves as a liaison with the department and works for a private company that they did not name. The work, Mr. Hecker and Mr. Patton said, “is perfectly legal, especially given his previous career as a N.Y.P.D. officer.”

Federal agents from the U.S. attorney’s office for the Southern District of New York and the Internal Revenue Service are conducting the investigation. Agents seized the phones of both Caban twins, according to two people with knowledge of the matter.

The police declined to comment. “Any questions regarding the investigation should be directed to the U.S. Attorney’s Office,” the department said in an email.

A spokesman for that office declined to comment. The I.R.S. did not immediately respond to a request for comment.

Police Department officials have said that federal investigators asked for the phones of several officers.

At least three — two lieutenants and a detective — have been contacted by federal agents, according to the person with knowledge of the investigation.

One lieutenant was served a subpoena by the I.R.S. to testify before a grand jury, the person said. The other lieutenant and the detective, who worked in the commissioner’s office, had their phones seized, the person said. Other department officials whose phones were seized include Mr. Caban’s chief of staff and two Queens precinct commanders, two other people with knowledge of the matter have said.

The detective contacted by federal agents is assigned to security details, said Scott Munro, the president of the police detectives’ union. The detective “is just a potential witness in whatever they’re looking into,” he said. “We’re confident our member has done nothing wrong.”

Mr. Hecker and Mr. Patton said that James Caban had a police security detail.

“The N.Y.P.D. protection provided to Mr. Caban was solely for his safety given his close relationship with his identical twin brother, Commissioner Caban, who faces numerous threats to his security given his position,” Mr. Hecker and Mr. Patton said in a statement. “Our client has fully cooperated with law enforcement and, once their investigation is complete, it will be clear that these claims are unfounded.”

The investigators are examining a wide range of information. According to the person with knowledge of the inquiry, they are seeking:

Records or evidence of payments from nightclubs, bars or restaurants to James Caban or to any members of law enforcement.

Evidence of any actions taken by members of law enforcement at the request of any nightclub, bar or restaurant.

Records of promotions or transfers of members of law enforcement.

Officers’ testimony surrounding the department’s rules and regulations around conflicts of interest and accepting gifts, services or money.

The two lieutenants who were contacted by federal officials work in special operations units of the department that are charged with responding to nightclubs, restaurants and bars that have chronic complaints against them.

None of the three officers are targets of the investigation, according to the person.

Chelsia Rose Marcius and Michael Wilson contributed reporting.