NEWARK — The two people who shot and killed a police officer and several civilians in Jersey City last month — before being killed themselves in a shootout with police — had a bomb that could have killed dozens more over an area the size of five football fields, the FBI said Monday.

The shooters also may have considered an attack at a Jewish community center in Bayonne, the FBI said.

And while officials have said David Anderson, 47, and Francine Graham, 50, had a history of anti-Jewish and anti-police sentiment, they weren't specifically gunning for Jersey City police detective Joseph Seals — killed by the pair before they headed to a kosher supermarket for the remainder of the massacre on Dec. 10, according to the FBI.

The FBI and U.S Attorney for New Jersey Greg Carpenito Monday disclosed several new details from their investigation about the shooting at the JC Kosher Supermarket on Martin Luther King Boulevard on Dec. 10, and the incidents connected to it.

'A cowardly act' planned for months

Anderson and Graham had been planning their attack for some time before they opened fire with rifles as they walked toward the market, where they killed Mindy Ferencz, 31, Douglas Miguel Rodriguez, 49, and Moshe Deutsch, 24, officials said.

Carpinito said an exhaustive investigation has led to the conclusion the shooting was a hate crime and an act of domestic terrorism.

It was a "cowardly act of anti-Semitism" and "anti-law enforcement," Carpinito said during a press conference at the FBI's office in Newark.

In March of 2018, Graham purchased five guns in a gun store in Ohio — including one of the firearms used on Dec. 10, Carpinito said. Graham rented a U-Haul van that had been used in the attack on Nov. 27, he said.

He said on December first, a week and a half before the attack, “we have reviewed video evidence of Graham and Anderson conducting target practice with long guns in Austintown, Ohio. It appears they traveled to Ohio, practiced at the shooting range, then traveled back to New Jersey.”

A few days later video surveillance shows the U Haul van driving around in Jersey City.

“It passed slowly on Dec. 4 and stopped in front of , on Dec 7, the Jersey City kosher supermarket that was ultimately the target of the Dec. 10 attack," Carpinito said.

The shooters also drove past the market twice the morning before the attack, he said.

Carpinito said investigators do not believe there area any co-conspirators in the shooting and no ongoing threat to Jersey City, though the investigation continues.

"We may never learn all the facts because everyone involved in shooting is dead along with the detective who questioned them in the cemetery," Carpinito said.

Cop wasn't a target

Carpinito said Seals had been at the Bay View Cemetery before the shooting on an unrelated case when he spotted a white U-Haul van that had been rented by Anderson and Graham. An alert had been issued to look out for the van, after it had been spotted at the scene where 34-year-old Jersey City resident Michael Rumberger was killed the weekend before. Authorities have said Anderson and Graham were the prime suspects in that case. The 34-year-old father of two's body was found stuffed in the trunk of his cab.

U.S. Army Corporal Yiesena Nunez, the mother of Rumberger's 17-year-old daughter, previously told New Jersey 101.5 she spoke with a detective in the case who told her that Rumberger picked up the couple at the Hudson Mall on Route 440 and then took them to White Glove Moving Co. in Bayonne, a ride of approximately 17 minutes.  She has said detectives have video showing Rumberger in a violent struggle Anderson and Graham before one of them shot him in the head.

Authorities have not yet made any statement as to why they believe Rumberger was killed.

During the cab ride, Anderson and Graham shot at a Hasidic Jewish man in another car, missing him but blowing out his windshield, Carpinito said. The man waited several days before reporting the incident to police, according to Carpinito.

Ballistics from that shooting matched the .22-caliber gun that was used to kill Rumberger, and again used in the Dec. 10 attacks at the kosher market, Carpinito said.

When Seals approached the van Dec. 10, Anderson and Graham opened fire, according to Carpinito. What exactly happened may never be known, because the shooters and Seals are all dead, but the pair is believed to have used a 9mm handgun to kill the detective, Carpinito said.

Carpinito said that Seals' death helped alerted police to Anderson and Graham -- and that the report of a police-involved shooting drew a rapid response.

“We believe that he threw Graham and Anderson off of what we’re piecing together now what was likely a broader plan, and probably led to saving dozens if not more lives," Carpinito said.

Hatred for 'wicked Israelites' and police

Carpinito said Anderson on social media called Jews "impostors who inhabited synagogues of Satan."  Anderson referred to the Jewish community as "wicked Israelites who loved darkness as cover for their wickedness," Carpinito said.

At the scene, a note found on Anderson contained a reference to a 1990s documentary, "The FBI's War on Black America," which explored the FBI's targeting of individuals involved in the civil rights movement in the 1960s, Carpenito said. He added that a timestamp written on the note corresponded to a segment in the documentary where an interviewee advocates killing "fascist pig cops."

Authorities have previously said Anderson appeared interested in the Black Hebrew Israelite movement. Some groups associated with the movement are regarded by experts as hate groups that reject mainstream Jewish movements as legitimate.

Carpentino said a note and bible found in the shooters van indicated they followed the Black Hebrew Israelite movement as well.

Huge potential for destruction

Anderson and Graham planned their attack on the planned for months, according to the officials. The were living in the the U-Haul van they had rented and bought five guns, Carpinito said.

Months before shooting they went to Ohio for shooting practice, though Carpinito did not say why.

Carpinito said investigators found a bomb in the van made up of "commonly acquired material" that could have spread shrapnel over an area the size of football fields, had it been detonated.

Investigators are not sure what Anderson and Graham's plan was for the bomb, but they found a Google search on on their phones for Jewish community centers nearby,  including one in Bayonne, according to Carpinito.

There was enough material in the van to make a second device, Carpinito said.

Anderson and Graham were found wearing tactical gear when their bodies were found after a shootout with police at the market, Carpinito said.

"Given the weapons they had, given the ammunition they had, it’s possible there were looking to target a larger community," he said.

Carpinito said the investigation is ongoing and urged anyone who may have seen anything  that may seem inconsequential may be valuable to investigators.

"If you think something is amiss, something is not right, reporting it allows law enforcement to do their jobs. They need the public's help," Carpinito said.

Material from the Associated Press was used in this report

Contact reporter Dan Alexander at Dan.Alexander@townsquaremedia.com or via Twitter @DanAlexanderNJ

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