"We continue to gather evidence related to motive," Efe news quoted Attorney General Gurbir Grewal as saying on Thursday.
"We believe the suspects held views reflective of hatred of the Jewish people and law enforcement.
"We believe the two shooters were acting on their own," he added.
Six people, including shooters David Anderson, 47, and Francine Graham, 50, died on Tuesday during a protracted gun-battle in Jersey City, just across the Hudson River from the New York City borough of Manhattan.
Anderson and Graham first killed Joseph Seal, a police detective who belonged to a unit responsible for removing illegal guns from the streets. They then fled the scene in a van and holed themselves up inside a kosher supermarket in the Greenville neighbourhood, which is home to a growing community of Orthodox Jews.
Two of the three people killed inside the store were Orthodox Jews, while the third was an Ecuadorian immigrant.
Grewal said that Anderson and Graham had shown interest in the Black Hebrew Israelites movement - regarded by some as a hate group - but authorities have yet to determine whether they had any formal ties to the organization.
Media outlets reported that FBI agents paid a visit Wednesday to the offices of the Black Hebrew Israelites in New York's Harlem.
Authorities recovered a total of five firearms, four inside the store and one in the U-Haul van used by the shooters.
The police also found a pipe-bomb inside the van.
Anderson entered the grocery carrying an AR-15 assault rifle, while Graham was armed with a Mossberg shotgun. Two 9 mm pistols were collected inside the supermarket and a 22-caliber handgun was left behind in the U-Haul.
A check of the serial numbers on the guns revealed that Graham purchased the shotgun and the 22-caliber handgun at separate stores in Ohio in 2018.
Investigators are convinced that Anderson and Graham deliberately targeted the Kosher grocery, Grewal said, because they waited until they were inside to start shooting, ignoring the pedestr outside.
The civilian victims were identified as the store's co-owner, Mindy Ferencz, and customers Moshe Deutsch and Miguel Douglas Rodriguez, who immigrated to the US from Ecuador three years ago with his wife and daughter.
Another civilian wounded in the shooting managed to flee the store.
( With inputs from IANS )