Religious writings on hate could be key to learning what motivated a pair of rifle-wielding suspects to kill three people in an attack on a Jewish market in Jersey City, New Jersey, after they allegedly gunned down a police detective in a cemetery, law enforcement sources told ABC News.

The suspects, David Anderson, 47, and Francine Graham, 50, were killed in a shootout with police on Tuesday but left a trail of potential evidence investigators are combing through to determine why they allegedly killed Jersey City Detective Joseph Seals and targeted the Jersey City Kosher Supermarket, officials said.

In a stolen U-Haul van, the suspects parked in front of the market just seconds before launching a rifle attack. Investigators found a pipe bomb and religious writings, including a handwritten note reading, “I do this because my creator makes me do this and I hate who he hates,” multiple law enforcement sources told ABC News.

Anderson and Graham are believed to have been members of the Black Israelites, a group that espouses hatred toward Jews and is known for anti-government and anti-police sentiments, sources told ABC News. Authorities in New Jersey did not have the Black Israelites on their radar as a violent group, more a nuisance at public events, the sources said.

At a news conference on Wednesday, New Jersey Attorney General Gurbir S. Grewal declined to speculate on a motive for the violence perpetrated by the suspects. But Jersey City Mayor Steven Fulop, the grandson of Holocaust survivors, told reporters “there is no question this is a hate crime.”

Grewal has scheduled a news conference for later Thursday to update the community on the case. The Federal Bureau of Investigation (FBI) and the U.S. Attorney’s Office for the District of New Jersey are also involved in the investigation.

Meanwhile, thousands of members of the Jewish Orthodox communities in Jersey City and Brooklyn, New York, gathered at cemeteries Wednesday night to mourn and bury two of the victims, 33-year-old Mindy Ferencz, the wife of the kosher supermarket owner and mother of five, and 24-year-old Moshe Deutsch, a Yeshiva student.

Deutsch’s father, Abe Deutsch, is a member of the United Jewish Organization’s board of directors, said Rabbi David Niederman, president of the organization.

“A few hundred bullets went into the body of a 24-year-old child … how can we as a community, as people, bear that?” Niederman said of Moshe Deutsch, during a news conference Wednesday at City Hall in New York City.

The third victim killed at the supermarket was identified by authorities as Douglas Miguel Rodriguez, 49, who worked at the store. Funeral arrangements for Rodriguez are pending.

A funeral for Seals, 39, a married father of five, is scheduled to be held next Tuesday.

The terrifying episode began to unfold about 12:38 p.m. on Tuesday when the Jersey City Police Department received a 911 call from an individual who discovered Seals’s body in the Bayview Cemetery, about a mile from the kosher market, Grewal said on Wednesday.

He said investigators believe Seals was shot to death when he confronted the suspects in the cemetery. He said Anderson and Graham were prime suspects in the murder this past weekend of an Uber driver officials identified as Michael Rumberger.

Rumberger’s body was found in the trunk of a Lincoln Town car around 10 p.m. Saturday, sources told ABC News.

Seals apparently had gone to the cemetery alone to meet the suspects and one of them may have been an informant he had worked with, possibly explaining why he felt comfortable meeting in the cemetery without backup or radioing in about the rendezvous, the sources said.

Seals, a plainclothes undercover detective, had been investigating the homicide, according to law enforcement sources.

After allegedly killing Seals in the cemetery, the suspects got into the stolen U-Haul van and drove to the kosher market, arriving about 12:43 p.m., Grewal said.

Security video, obtained by ABC News, shows the suspects parking directly across the street from the supermarket on Martin Luther King Drive, getting out of the vehicle holding rifles and calmly walking into the supermarket as passersby on the street scrambled for cover.

Grewal said four people, including the three slain victims, were inside the store when the suspects stormed through the front door. A lone survivor, who was shot and wounded, managed to escape, Grewal said.

Two foot patrol officers were about a block from the deli and responded as soon as they heard the gunfire, Grewal said. They were both shot and wounded in a gunfight with the suspects that involved other Jersey City police officers, he said.

The gunbattle lasted until about 3:47 p.m. when a police armored vehicle broke through the entryway of the supermarket and police found the bodies of the suspects and the three victims inside.

In addition to the two other officers wounded in the shootout, a third was hurt by shrapnel, officials said. The officers were all treated at a hospital and released.