An assailant involved in the prolonged firefight in Jersey City, N.J., that left six people dead, including one police officer, was linked on Wednesday to the Black Hebrew Israelite movement, and had published anti-Semitic posts online, a law enforcement official said.

The violent rampage on Tuesday took place largely at a kosher supermarket where three bystanders were killed. The authorities now believe that the store was specifically targeted by the assailants, whom they identified as David N. Anderson, 47, and Francine Graham, 50.

Mr. Anderson appeared to have a connection to the Black Hebrew Israelite movement, though the extent of his involvement in that group remains unclear, the law enforcement official said.

The Black Hebrew Israelites, which has no connection with mainstream Judaism, has been described as a hate group by the Southern Poverty Law Center, a legal advocacy group that tracks such movements.

The authorities also suspected that the two assailants may have been involved in a separate killing in neighboring Bayonne, N.J., according to New Jersey’s attorney general, Gurbir S. Grewal.

Among those killed on Tuesday were three bystanders who were inside the store when the shootout began. They have been identified as Mindel Ferencz, 33, who ran the market with her husband; Moshe Deutch, 24, a rabbinical student who lives in Brooklyn; and Miguel Douglas Rodriguez, 49, who may have worked at the store.

One other person inside the store was wounded but managed to escape, according to Mr. Grewal.

The Jersey City police officer who was killed was identified on Tuesday as Detective Joe Seals, a 15-year law enforcement veteran and a father of five.

An assailant had links to the Black Hebrew Israelites.

Investigators also found a live pipe bomb inside the vehicle, officials said on Wednesday.

Jersey City’s mayor, Steven Fulop, said that Mr. Anderson’s online posts included “favorable sentiment” toward anti-Semitic groups, shared on Facebook.

While the exact beliefs of the Black Hebrew Israelites vary among the groups associated with the movement, followers generally believe that the 12 tribes of Israel defined in the Old Testament are different ethnic groups, or nations, and that white people are not among them.

“They mostly trade in anti-Semitism,” said Heidi Beirich, the director of the Intelligence Project at the Southern Poverty Law Center. “They view Jews as impostors.”

She added that the movement has not been known for committing mass acts of violence.

At a news conference on Wednesday, Mr. Grewal said he would not comment on the assailants’ motives.

“We are working to learn more about the shooters’ motivations, and whether anyone besides the two gunmen may have been involved,” Mr. Grewal said.

But Mr. Fulop, a grandson of Holocaust survivors, said he and other Jersey City officials had no doubt the attack was a hate crime.

“There is no question that this is a hate crime,” Mr. Fulop said. “And anti-Semitism should be called out aggressively and firmly — immediately — for what it is.”

Officials said they did not believe there was any ongoing security threat related to Tuesday’s events.

A neighbor knew one of the suspects, and saw a change.

David N. Anderson was in the Army Reserve from September 1999 to September 2003 and achieved the rank of specialist, according to an Army spokesman. He repaired fuel and electrical systems.

Mr. Anderson had a criminal record for previous weapons offenses in Hudson County in both 2004 and 2007. He spent more than a year in jail on the 2007 weapons charge, according to court records.

In 2017, he and Francine Graham met, according to a neighbor of Ms. Graham’s who said he had lived above her since 2011.

When Ms. Graham moved into a housing development in Elizabeth, N.J., from the block in Harlem where she grew up, she was a polite, diligent, hardworking home health aide, said the neighbor, who did not wish to be named.

“She was nice, she had a caring nature, she was a standup person,” he said.

But after meeting Mr. Anderson, she changed, the neighbor said, describing her transformation as “Jekyll and Hyde.”

Mr. Anderson seemed to move in with Ms. Graham within days of meeting her. The neighbor described Mr. Anderson as a “loser,” “not pleasant” and “kind of overpowering” and someone with whom he had “squabbles.”

The neighbor said Mr. Anderson seemed both to “prey on” and control Ms. Graham.

“David came out of nowhere and flipped her life around,” he said, adding, “It was like we didn’t know her anymore.”

Sometime after Mr. Anderson moved in, the neighbor began hearing noises from downstairs.

Mr. Anderson repeatedly played audio recordings of a man the neighbor believed to be Louis Farrakhan, and sounded like he himself was growing agitated. He shouted bible verses and then chanted out his interpretations of what they meant.

The neighbor said the most common theme was that Mr. Anderson’s religion was the only true faith while others — specifically Catholicism and Judaism — were false.

He soon heard Ms. Graham join in the chanting and said she sounded “coerced.”

She quit paying her common charges for the condominium they shared and also stoped paying her water bill, he said.

Eventually, in 2018, her condo unit went into foreclosure, the neighbor said. She and Mr. Anderson were evicted, but they repeatedly busted into their former home to spend the day there, leaving each day around 6 p.m.

As for Ms. Graham, he said he had not seen her in a year. He learned of the Jersey City shooting when the police banged on his door at 2:30 a.m.

Mayor Fulop said on Wednesday that surveillance footage revealed that after the two assailants shot Detective Seals in an encounter at a cemetery, they drove slowly and deliberately to the kosher market, roughly a mile away.

“The perpetrators stopped in front of there and calmly opened the door with two long rifles,” he said.

Mr. Fulop and Jersey City’s public safety director, James Shea, said that after the attackers left the van, they walked past others on the street and aimed at people inside the kosher supermarket.

“We now know this did not begin with gunfire between police officers and perpetrators and then moved to the store,” Mr. Shea said. “It began with an attack on the civilians inside the store.”

Initially, investigators said they believed that the attackers randomly chose the market and that the episode was not a hate crime; Mr. Shea added on Tuesday that there was “no indication” of terrorism.

By that night, however, Mr. Fulop, said on Twitter that officials had come to believe that the assailants had “targeted the location they attacked.”

Detective Joseph Seals approached the two assailants, who were inside a U-Haul van near a cemetery, because the van had been linked to a homicide over the weekend, according to the law enforcement official.

Investigators believe the assailants then shot the detective. Video surveillance footage shows them driving away, toward the kosher market.

Around 12:30 p.m., the authorities were alerted about a shooting at the market, at the same time hearing about the detective being shot, officials said. Two police officers who were on a foot patrol nearby immediately responded to the call and were met with gunfire. Both the officers were injured but in stable condition, officials said.

For much of at least the next hour, residents nearby — and blocks away — could hear rapid bursts of gunfire coming from the area around the market.

As the prolonged firefight went on, helicopters circled overhead as police officers swarmed the streets. They aimed handguns and long guns in every direction as they traveled down the street in formations, knocking on doors and rushing residents and business owners to safety.

“This is one of the biggest gunfights I’ve seen in a while,” said Willy McDonald, 67, who lives in the area. “And I’ve been in Vietnam.”

Surveillance footage shows shooters entering the store.

Camera footage of Martin Luther King Drive that was circulating on social media on Wednesday showed the moment the two assailants entered the kosher supermarket.

In the footage, the pair parked a white van across the street from the market. The driver almost immediately bounds out of the vehicle with a long gun pointed toward the building.

Pedestrians appear to scramble frantically for safety, some fleeing down the street and others weaving behind cars for cover. Behind the driver, a passenger who appears to have a weapon also follows more slowly, only dashing into the store after the driver has entered.

Just moments later, an agitated man runs out of the store.

It was unclear whether the footage in the video was the one referenced by Mr. Fulop.

Two members of the Hasidic community and a worker were killed.

Hasidic community leaders on Wednesday morning identified the two members of their community who were killed.

Mindel Ferencz, whose family owned the kosher market, was working at the store at the time of the attack.

About five years ago, she and her husband were among the first Hasidic Jews to relocate to Jersey City from Williamsburg, Brooklyn. The couple had three children, said Rabbi Mordechai Feuerwerker, a community leader.

The victim’s mother-in-law, Victoria Ferencz, 72, heard the news on Wednesday morning from Jewish media. “I’ve cried my eyes out already. I’m feeling pretty broken,” she said. “I feel sorry for my son. She’s going to heaven, but he and his children will have it hard.”

At the time of the shooting, she said, her son had gone to a nearby synagogue and his wife was tending the market. Shots rang out, and the synagogue was put on lockdown.

Shaya Bodenstein, 41, who often went to the market, said Ms. Ferencz would always help her husband at the register whenever he stepped out to pray or deliver groceries.

Mr. Bodenstein also said that he met Douglas Miguel Rodriguez, who went by his middle name, while frequenting the store over the years.

“Miguel was a very nice, quiet guy,” Mr. Bodenstein said outside of the store, which was covered with wooden planks on Wednesday afternoon. “I used to see him all the time — always helping.”

Another victim was Mr. Deutsch, 24, the rabbinical student.

At a news conference in Manhattan, Rabbi David Niederman described Mr. Deutsch as “extremely kind and generous” and a “go-to person when his peers needed help.”

Rabbi Niederman, the president of the United Jewish Organizations of Williamsburg, said Mr. Deutsch had helped lead a food drive this year and helped to feed 2,000 people.

As he spoke about the young victim, the rabbi choked up.

“Can you imagine a few hundred bullets went into the body of a 24-year-old child?” he said.

On Wednesday morning, detectives were at the Jersey City Kosher Supermarket, canvassing the crime scene as a number of uniformed police officers stood watch outside.

Officers also believe the two attackers in Jersey City were connected to the death of another Jersey City resident who was found beaten to death in the trunk of car in nearby Bayonne on Saturday night.

The man, Michael Rumberger, 34, was found inside a Lincoln Town Car with “massive head trauma,” according to the Hudson County prosecutor’s office.

Mr. Grewal, the state’s attorney general, said that Mr. Anderson and Ms. Graham were currently the “prime suspects” in the case.

The market was part of a budding Jewish community.

The shootout and police siege overtook the Greenville neighborhood of gentrifying Jersey City — the second most-populous city in New Jersey, with about a quarter of a million residents.

The supermarket caters to a small but steadily growing community of Hasidic families who have moved to Jersey City in recent years from the Williamsburg neighborhood in Brooklyn.

These families, many of whom belong to the ultra-Orthodox Satmar sect, have created a budding community in Greenville, a residential area with a historically African-American population.

The opening of the kosher market three years ago signaled to some that the growing Jewish population was putting down roots in the area.

The detective killed was a longtime police veteran.

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Detective Seals had been a police officer for 15 years, said Chief Michael Kelly. He rose through the ranks of the Jersey City Police Department, coming to work in the city’s busy South District.

After being promoted to detective in 2017, he was most recently assigned to a citywide unit tasked with making gun arrests in Jersey City.

Detective Seals lived in North Arlington, N.J., a suburb about eight miles northwest of Jersey City, with his wife and five children, the youngest of whom was 2 years old.

His mother, Deborah Ann Perruzza, 65, said that Detective Seals “always wanted to be a cop.”

On Tuesday, Ms. Perruzza said that when she arrived at Jersey City Medical Center, doctors told her that her son had been shot twice, including once in the back of the head.

Nick Corasaniti, Corina Knoll, Jeffery C. Mays, Sarah Maslin Nir, Sharon Otterman, Azi Paybarah, Ed Shanahan, Edgar Sandoval, Nate Schweber, Ashley Southall, Tracey Tully and Michael Wilson contributed reporting. Susan C. Beachy and Jack Begg contributed research.