NEW YORK (Reuters) - Investigators are not sure why two people launched a deadly attack at a New Jersey kosher grocery store, federal and state officials said on Wednesday, but a federal law enforcement source said it did not appear to be an act of terrorism.

Six people, including the two shooters, three civilians and a police officer, died in a series of events that ended in a police shootout on Tuesday in Jersey City, New Jersey, across the Hudson River from New York City.

The four-hour gun battle at the Jewish JC Kosher Supermarket erupted after the pair shot the police officer at a nearby cemetery and then fled in a white van. It ended after police crashed an armored vehicle through the wall of the market.

“We are not in the position at this time to say definitively why the suspects stopped in front of the supermarket and began firing,” New Jersey Attorney General Gurbir Grewal told a news conference, flanked by state and federal colleagues.

Jersey City Mayor Steven Fulop reiterated in a later news conference that he considered the shooting a hate crime.

“My sentiment is that it should be viewed as a hate crime and called out aggressively and called out quickly,” Fulop said, without providing evidence.

The federal law enforcement source said investigators believe mental illness and drug use may have been the primary factors in the attack. He said investigators now view an anti-Semitic message posted online by one of the shooters as a secondary factor.

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Officials identified the shooters as David Anderson, 47, and Francine Graham, 50. The three civilian victims inside the market were Mindy Ferenz, 32, Miguel Douglas, 49, and Moshe Deutsch, 24, they said.

A fourth person who was in the market when the shooters entered escaped. Officials declined to identify that person.

Police found a homemade pipe bomb in the rented van that the shooters drove to the market.

The initial confrontation between the suspects and police near the Jersey City cemetery, about a mile (1.6 km) from the supermarket, was linked to a previous homicide investigation, officials said.

The dead police officer, identified as Joseph Seals, a 15-year veteran of the force and father of five, was shot at the cemetery.

“We are deeply shocked and saddened by the antisemitic attack in #JerseyCity yesterday,” the Israeli embassy in Washington said on Twitter.

“This remains a very fluid and fast-moving investigation,” said New Jersey Governor Phil Murphy. “There is no ongoing security concern.”