One of the two suspects who killed a police officer before targeting a kosher grocery store in Jersey City, New Jersey, where three people were killed had a social media page containing anti-Jewish and anti-police writings, officials and sources said Wednesday.

Authorities identified the suspects as David Anderson, 47, and Francine Graham, 50.

Jersey City Police Detective Joseph Seals was killed Tuesday shortly before officials say the suspects attacked the store. The victims in the store were identified Wednesday by authorities as Mindy Ferencz, 31; Miguel Douglas, 49; and Moshe Deutsch, 24.

According to three sources, Anderson was a one-time follower of the Black Hebrew Israelite movement, whose members believe they are descendants of the ancient Israelites, and his social media pages include anti-police and anti-Jewish writings. Investigators are looking to see if it was Anderson himself who posted that material.

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Inside the van used by Anderson and Graham was a note with religious writings, the three sources said.

David Anderson. Obtained by NBC News

The deadly attack began Tuesday afternoon when Anderson and Graham encountered Seals in a cemetery, Attorney General Gurbir S. Grewal said at a news conference Wednesday afternoon.

Grewal said it's believed that the suspects killed Seals at the cemetery, then got in a U-Haul van and drove about a mile away to the JC Kosher Supermarket. The shooters parked across the street from the store and seconds later Anderson exited the driver's side of the vehicle armed with a long gun.

He immediately began firing at the store as he walked inside, Grewal told reporters. Graham exited the van and followed Anderson inside, but Grewal would not say if she was also armed.

What followed was an hourslong standoff and shootout between police and the suspects. Just before 3:30 p.m., authorities used an armored police vehicle to break into the entrance of the store, Grewal said.

Authorities said "numerous firearms" were found at the scene and a pipe bomb was found in the van driven by Anderson and Graham. Gregory W. Ehrie, with FBI Newark, said the device was "viable," meaning it could have exploded.

Earlier Wednesday, Jersey City Mayor Steven Fulop said that security footage showed the shooters traveling slowly through the streets in the van before stopping outside the store.

"There were multiple other people on the streets," Public Safety Director James Shea said. "There were many other targets available to them that they bypassed to attack that place. So it was, clearly, that was their target, and they intended to harm people inside there."

Shea emphasized that the shooters' motive is not yet clear and is under investigation.

Grewal said both Anderson and Graham were suspects in the recent killing of an Uber driver in Bayonne, New Jersey.

The bodies of three civilians were found inside the store. A fourth person was shot, but was able to escape and is recovering.

Anderson and Graham were also found dead.

Jail records show that Anderson was arrested in New Jersey on weapons charges stemming from a 2007 incident and in Ohio for criminal mischief stemming from a 2009 incident. He also had a run-in with the law in 2004 and was sentenced to three years of probation.

Ronald S. Lauder, founder of the Anti-Semitism Accountability Project, condemned the attack as "yet another example of how Jews are being violently targeted" across the country.

"It’s time to hold elected officials accountable: If you enable anti-Semitism or fail to take it seriously, we will see to it that you lose re-election," Lauder said in a statement. "We will see to it before other communities become memorials. Looking the other way never has – and never will – end well.”

On Tuesday, sources and officials said Seals was killed after police investigating a murder approached the two suspects and one of them opened fire, hitting the officer in the head. Police Chief Mike Kelly said that authorities believe the detective was shot while trying to stop the suspects.

Shea and Fulop declined to discuss Wednesday how the detective's death may have been connected to the grocery store shooting.

Seals had been with the department since 2006 and was a married father of five.

In a tweet Tuesday, Fulop called Seals a "great cop," saying he is probably "responsible for more guns being removed from the streets than any. He was an officer that loved JC, was involved in the city, and one that everyone knew regardless of their precinct."

Shea told reporters Wednesday that police in the area responded to the store immediately, probably saving more people from being killed.

"The streets were filled with people and the school was filled with people, and we have to assume that they would have continued attacking people," he said.