(CNN) This week's deadly kosher market attack and the killing of a detective in New Jersey are being investigated as acts of domestic terrorism "fueled by both anti-Semitism and anti-law enforcement beliefs," the state attorney general said Thursday.

"We believe the suspects held views that reflected hatred of the Jewish people, as well as a hatred of law enforcement," New Jersey Attorney General Gurbir S. Grewal said, citing evidence and witness interviews.

Investigators believe David N. Anderson, 47, and Francine Graham, 50, killed a police detective near a Jersey City cemetery and then stormed a nearby Jewish market Tuesday, shooting and killing three people there and starting an hourslong police standoff that ended with their deaths, authorities said.

It's still not known why Anderson and Graham attacked the detective and the JC Kosher Supermarket in particular, Grewal said.

But evidence points to these being "acts of hate," Grewal said in a news conference in Jersey City. The FBI is investigating the shootings as "domestic terrorism with a hate-crime bias slant to it," said Gregory Ehrie, special agent in charge for the FBI in Newark.

Investigators think Anderson and Graham acted by themselves, Ehrie said.

While both shooters have expressed interest in the Black Hebrew Israelites movement, neither appear to have established formal links to the movement, Grewal said. Grewal didn't specify evidence pointing to a hate crime, though he said social media accounts believed linked to the shooters "espouse certain viewpoints."

Grewal and others stressed that once at the market, the shooters apparently fired only at people there, and at responding police officers, bypassing multiple opportunities to shoot others on the street.

"They were clearly targeting that store. They were clearly targeting the Jersey City Police Department," US Attorney Craig Carpenito said, partly citing surveillance video.

Investigators are checking killers' ties to a previous killing and anti-Semitic writings

Anderson and Graham also were suspects in the weekend killing of a livery driver near the neighboring New Jersey city of Bayonne, Grewal has said. That man died Saturday, local media outlets, including NJ.com , reported.

Authorities haven't said what, if anything, links the weekend killing to Tuesday's shootings, other than investigators believe Anderson and Graham were behind them all.

Investigators also checking a note found a stolen U-Haul truck that the killers parked across from the market -- a note that contained both anti-Semitic and anti-police writing, a law enforcement source told CNN.

Posts with similar sentiments also have been found on social media linked to the shooters, the source said.

"Our community has been terrorized once again by violent anti-Semitism," Jonathan Greenblatt, CEO of the Anti-Defamation League, said in a statement. "From Pittsburgh to Poway , and now to Jersey City, the disease that is anti-Semitism has clearly spread to epidemic proportions."

"But we will not be defeated, we will not stand down, we will not be intimidated," Greenblatt said.

Shooters had lots of firepower and 'could have done more' had police not stopped them

Killed Tuesday were Jersey City police Detective Joseph Seals and three people in the market: Mindy Ferencz, 31, the store's co-owner; Moshe Deutsch, 24, a customer; and Douglas Miguel Rodriguez, 49, a store employee.

One person who was inside the market was shot when Anderson and Graham opened fire, but he fled the store as the attackers shot at him, and survived, officials said.

Investigators think all three slain victims in the store "were shot ... within minutes of the shooters entering the store," Grewal said.

Hundreds of ammunition shells have been recovered from the market scene, Grewal said.

Grewal on Thursday gave this account of the attackers' weapons found in the store:

• An AR-15-style weapon, which Anderson fired as he entered

• A Mossberg 12-gauge shotgun, which Graham carried into the store

• A 9mm Ruger semiautomatic firearm

• A 9mm Glock 17

Inside the killers' stolen U-Haul across the street was a pipe bomb and a fifth gun -- a .22-caliber Ruger with a homemade silencer and a homemade device to catch shells, Grewal said.

The U-Haul also had "ballistic panels" designed to resist damage, Grewal said.

"But for the actions of (police), they (the attackers) could have done more," Grewal said.

Graham bought the shotgun and the Ruger in Ohio in the spring of 2018, the attorney general said.

Tracking the shooters from a cemetery to the market

Before Anderson and Graham made their way to the kosher market, they are believed to have killed Seals near a city cemetery, authorities have said.

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Police have said Seals was trying to stop Anderson and Graham -- but they haven't said why he tried, or why Anderson and Graham killed him.

A bystander called 911 to report Seals' body at the cemetery at 12:38 p.m., authorities said.

By that time, Anderson and Graham already were attacking the market.

Surveillance video shows Anderson parking a stolen U-Haul across the street from the JC Kosher Supermarket, about a mile from the cemetery, city officials say.

The pair get out, and a man -- Anderson, police say -- walks directly toward the store , apparently ignoring several people on the sidewalk nearby, and starts firing a gun into it before entering. Graham follows, police say.

Police say Anderson, right, started firing seconds after exiting a stolen vehicle.

Jersey City Mayor Steven Fulop has cited this video -- appearing to show Anderson ignoring pedestrians and other businesses -- as evidence that he attacked the kosher store for specific reasons.

"My sentiment is that it should be viewed as a hate crime," Fulop said Wednesday afternoon. "There's no question it was an attack on the Jewish community."

Police arrived at the supermarket around 20 minutes after the attack began, starting a long shootout that left two police officers injured.

Around 3:25 p.m., a police armored vehicle broke into the supermarket's entryway, and law enforcement soon found the bodies of the three victims and two attackers inside the store, Grewal said.

Investigators checking shooter's connection to Black Hebrew Israelites and anti-Semitic notes

A law enforcement official told the New York Times Wednesday that Anderson appears to have a connection with the Black Hebrew Israelites movement, but the extent is unclear.

David Anderson

The Black Hebrew Israelite movement is best known for its confrontational brand of street preaching in urban areas but it has a complex history in the United States, with sects and branches splintering over theological and leadership disputes. Scholars say what unites most Black Israelites is the belief that African-Americans are the true descendants of biblical Jews.

Some members have expressed anti-Semitic sentiments in the past.

Anderson served in the US Army Reserve from September 1999 to September 2003, the Army said, as a fuel and electrical system repairer.

Funerals guarded by police and volunteers

Orthodox Jewish men mourn during the funeral service of Mindy Ferencz who was killed in a kosher market that was the site of a gun battle in Jersey City, New Jersey.

Two of the four victims were laid to rest Wednesday night.

In Jersey City, crowds of men in black hats surrounded Ferencz's casket in the Jersey City neighborhood of Greenville at the site of a synagogue under construction. Hundreds of women, separated from the men as per Orthodox Jewish tradition, were standing in the bitter cold sobbing.

Ferencz owned the store with her husband, who was next door at the small synagogue at the time of the attack, according to Yossi Steinmetz who was there as well.

When shots broke out, her husband desperately tried to call her and tell her to lock the doors to take cover, Steinmetz said. She didn't answer.

At Deutsch's Brooklyn funeral, mourners spoke in Hebrew through tears as at least a dozen NYPD counterterrorism officers and nearly 100 "Shomrim" members -- Hebrew for guardians -- stood watch.

Thousands of Orthodox Jewish men crowded Rodney Street in Williamsburg, Brooklyn.

Deutsch and Ferencz both had ties to the Jewish community in the Williamsburg neighborhood of Brooklyn, New York City Mayor Bill de Blasio said.

"This is just an atrocity. Of course, we accept everything but this is more than we can handle," Deutsch's cousin, also named Moshe Deutsch, told CNN. "The question is, is it a sign of hatred? Is it a sign that we are not safe in New York anymore?"