The suspects in last month's deadly shooting at a kosher grocery store in New Jersey had an explosive device hidden in their vehicle that could have killed or maimed dozens of people, FBI officials said Monday.

FBI officials and the U.S attorney's office for the district of New Jersey told NBC News that the device, described as a crude pipe bomb, could have killed bystanders or wounded people up to 500 yards away.

Authorities have identified David N. Anderson and Francine Graham as the two suspects in the December shooting that left six dead including both of them. Anderson and Graham were suspected members of the Black Israelite movement, which has been designated by the Southern Poverty Law Center (SPLC) as an anti-Semitic and black supremacist hate group.

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At least two of those killed were members of Jersey City's Hasidic community, according to news reports. Also among the dead was Joseph Seals, a local police detective.

"We believe he threw off a broader plan," U.S. attorney Craig Carpenito said of Seals, adding that he "probably saved dozens if not more lives."

Other weapons were also reportedly found in the suspects' van, which was outfitted with special ballistic panels, according to NBC.