A police officer, three civilians and two suspects were killed Tuesday afternoon during a shootout and standoff in Jersey City, New Jersey, authorities said. The deadly mayhem started when the slain officer was investigating a murder and approached two suspects — when one of them opened fire, shooting the officer in the head and killing him, law enforcement sources told NBC News. The two suspects then fled in a rental van and holed up in a grocery store a few blocks away, near Martin Luther King Drive and Bidwell Avenue, about 8 miles southwest of Midtown Manhattan in New York City, law enforcement sources said. The suspects and three civilians were killed inside that grocery store in the ensuing gunbattle, sources said. The 39-year-old officer who was killed has been identified as Det. Joseph Seals, who was with the Jersey City Police Department since 2006. Seals was married and the father of five children. Though the investigation is still in its early phases, Jersey City Police Chief Mike Kelly said authorities believe Seals was shot while trying to stop the suspects. Kelly said that while he was unsure why the plainclothes detective was there, he believes it may have been related to guns. "As the mayor alluded to, he was the leading police officer in removing guns from the street," Kelly said. "Dozens and dozens of handguns, he’s responsible for removing from the street." Two other officers were injured, one in the shoulder and one in the body, but have since been released. SWAT officers and first responders, including Hatzalah paramedics, who serve the orthodox Jewish community, rushed to the scene. "Our thoughts and prayers are with the men and women of the Jersey City Police Department, especially with the officers shot during this standoff, and with the residents and schoolchildren currently under lockdown," New Jersey Gov. Phil Murphy said in a statement. "I have every confidence in our law enforcement professionals to ensure the safety of the community and resolve this situation. Today reminds us of their bravery and the sacrifices they, and their families, make for our communities." All schools in Jersey City were put on lockdown, while campuses in nearby Bayonne were under a "shelter in place" order as a precaution, officials said. The Jersey City School District first tweeted about the lockdown at 1:30 p.m. and students were not reunited with parents until nearly 5 p.m. SWAT teams with Jersey City and state police were among those responding. Federal agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives in Newark and the FBI were also on the scene. “I can hear the gunshots. It's like firecrackers going off," said Andy Patel, who works at a liquor store about three blocks from the scene. "They were shooting like crazy about an hour ago. Then it stopped for like 20 or 30 minutes. The cops were clearing everyone off the streets."