The deadly rampage that ended with one police officer slain and three bystanders killed at a kosher market in New Jersey is now being treated as an act of domestic terrorism, the authorities said on Thursday.
Investigators believe the two attackers were “fueled both by anti-Semitism and anti-law enforcement beliefs,” New Jersey’s attorney general, Gurbir S. Grewal, told reporters at a news conference.
As a result of the evidence so far, the F.B.I. was investigating the violence as “a domestic terrorism incident with a hate crime bias,” said Gregory W. Ehrie, the special agent in charge of the bureau’s office in Newark.
After initially calling the attack on the JC Kosher Supermarket in Jersey City on Tuesday a random act, investigators said that the store had been deliberately targeted but did not explicitly say it was motivated by anti-Semitism.
Even as it emerged that one of the two attackers, David N. Anderson, had published anti-Semitic posts online and had ties to a movement that has expressed hostility toward Jews, federal and state authorities shied away from calling the assault a bias crime.
But on Thursday, Mr. Grewal confirmed that investigators believed Mr. Anderson and his accomplice, Francine Graham, both of whom were killed in the firefight, held views that “reflected hatred of the Jewish people, as well as a hatred of law enforcement.”
He also said that investigators had found four firearms belonging to the assailants inside the supermarket, including an AR-15-style weapon and a shotgun, as well as an additional gun and a pipe bomb inside a rental van the assailants had been driving.
“They had a tremendous amount of firepower,” Mr. Grewal said.
The developments came as residents of Jersey City, located across the Hudson River from Lower Manhattan, were reeling from the chaos on Tuesday, when a fierce firefight put parts of the city on lockdown.
Officials believe that the fusillade began when Mr. Anderson and Ms. Graham’s vehicle was approached by Detective Joe Seals at a cemetery. Detective Seals apparently recognized their van from a bulletin related to the killing last weekend of a 34-year-old man in nearby Bayonne, N.J.
After shooting Detective Seals, Mr. Anderson and Ms. Graham drove about a mile to Jersey City’s Greenville neighborhood, the center of a growing Hasidic community, and parked across the street from the kosher market.
According to surveillance video, the two jumped out of the vehicle with their weapons pointed at the store. They stormed into the market, ignoring others on the street, and began firing, officials said.
On Thursday, Mr. Grewal said investigators believed that the three people slain inside the store — Leah Mindel Ferencz, Moshe Deutsch and Douglas Miguel Rodriguez — were killed within minutes of the assailants’ entrance. Then, Mr. Anderson and Ms. Graham began firing at police officers who were responding to calls about shots being fired.
By that point, Mr. Grewal said, “the shooters were aiming their fire at law enforcement officials only, and not at others on the street.”
Inside the supermarket, investigators found an AR-15-style rifle and a 12-gauge shotgun that they believed Mr. Anderson and Ms. Graham carried into the store. They also found two 9-millimeter semiautomatic pistols.
Inside the rental van, investigators found another weapon, a Ruger Mark IV with a homemade silencer and a homemade device to catch shell casings, Mr. Grewal said. It was also outfitted with ballistic panels, which are typically used to defend against bullets.
Investigators traced the serial numbers on two of the weapons and believed that Ms. Graham bought them in at different stores in Ohio in 2018, Mr. Grewal said.
Officials also said they had reviewed social media posts made by Mr. Anderson and Ms. Graham that expressed anti-Semitic and anti-police views.
Both attackers, they said, had expressed interest in the Black Hebrew Israelites, a religious movement with dozens of groups that believe, in general, that the chosen ones are black, Native American and Hispanic people, but not white people.
While the movement is not known for promoting violence, some of its offshoots have been described as hate groups by the Southern Poverty Law Center, a legal advocacy organization that tracks such movements.
Investigators had not established any formal connections between Mr. Anderson and Ms. Graham and any specific Black Hebrew Israelite groups, Mr. Grewal said.
“We believe that the two shooters were acting on their own,” he said.
Law enforcement officials had previously said that a brief but rambling religious manifesto-style note was found inside the attackers’ van. It did not establish a clear motive for the shooting, but in nearly illegible handwriting, it indicated that Mr. Anderson believed he was charged with carrying out “God’s will,” they said.
The governor of New Jersey, Philip D. Murphy, said Tuesday’s attack reflected a growing crisis of intolerance.
“The murder of innocent civilians because of their religious beliefs, and the murder of a police officer for the simple reason that he was a police officer,” he said in a statement, “must be the wake up call to those who fail to see or acknowledge the rising tide of hate here in New Jersey, and around the nation.”