The two assailants who shot up a Jersey City, N.J., kosher grocery cased the shop for months ahead of the attack, made a bomb strong enough to injure and kill people up to five football fields away and researched other Jewish centers, officials said.
The two shooters also shot out the back window of a vehicle driven by a Hasidic Jewish person in the area of Newark and Elizabeth in early December, law-enforcement officials said for the first time at a news conference on Monday. The driver reported the incident after the grocery store shooting, and law-enforcement officials recovered a bullet from the vehicle that matched those used by the assailants, officials said.
Days before the shooting, the assailants practiced at a firing range in Ohio, officials said. There was no evidence that the assailants targeted the yeshiva next door to the grocery store, officials said, but investigators found that the shooters made online searches for a Jewish community center in Bayonne.
Video footage also shows that the assailants cased the store twice in the days leading up to their Dec. 10 attack that left four people dead, including two Jewish people. Police killed the assailants after an hourslong standoff where the shooters fired hundreds of rounds.
“We now know they planned greater acts,” said Craig Carpenito, U.S. attorney for the district of New Jersey at the news conference. “This was in fact a hate crime and an episode of domestic terrorism.”
New Jersey Attorney General Gurbir Grewal said the attack on the Jersey City grocery store coincided with a surge in bias incidents in the state, which he described as a “rising tide of hate and intolerance.”
There were 944 bias incidents in New Jersey in 2019, a 65% jump from the previous year and the single largest year-over-year increase in the state’s history, Mr. Grewal said. Many of those involved anti-Semitic incidents, he said.
“These are more than troubling,” Mr. Grewal said. “They are unacceptable.”
The shooters have also been identified as prime suspects in the killing of Michael Rumberger, 34 years old, of Jersey City. The assailants made online searches for news of the killing of the livery driver, but investigators haven’t found a prior connection between the shooters and the driver, officials said.
The shooters may have rushed their attack plans the day of the shooting after they were confronted by Jersey City Police Detective Joseph Seals in a cemetery about a mile from the kosher grocery store, officials said. A notice had been issued alerting police officers to be on the lookout for a white U-Haul van following the killing of Mr. Rumberger.
The shooters rented the van and had been living out of it, officials said. Detective Seals may have noticed the van in the cemetery and approached it before the assailants shot and killed him, officials said.
One of the shooters was found with a note that read “The FBI’s war on black America,” which is the name of a documentary film. The note also referenced a time stamp of 34:35. At that point in the film, a member of the Black Panther Party is speaking and makes statements against police, officials said.
While investigators said the shooters expressed interest in the Black Hebrew Israelites, they didn’t find formal links to the religious group.
Gregory Ehrie, special agent in charge of the Federal Bureau of Investigation’s Newark office, said that despite the shooters’ months of planning, there were no red flags that would have raised any alarms with law enforcement.
“Up until this attack, there is nothing that would have put these two individuals on anybody’s radar,” Mr. Ehrie said.
Write to Joseph De Avila at joseph.deavila@wsj.com
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