Six people, including a police officer and three bystanders, were killed in a furious gun battle Tuesday that filled the streets of Jersey City with the sound of heavy fire for hours. The dead included the two gunmen.

The slain officer, Detective Joseph Seals, 40, was credited by his superiors with having led the department in the number of illegal guns removed from the streets in recent years, and might have been trying to stop an incident involving such weapons when he was cut down by gunfire that erupted near a cemetery, authorities said.

The shooting then continued at a kosher supermarket about a mile away, where five more bodies were found, Kelly said.