The attacker, who served in Afghanistan and Iraq, also wounded an 11-year-old girl with seven gunshots.
President Joe Biden has toured flood damage in New Jersey and says he was thinking about the all families who suffered “profound” losses from the powerful remnants of Hurricane Ida.
Biden also planned to visit New York City on Tuesday, to survey the aftermath and call for federal spending to fortify infrastructure to better defend people and property from future storms in the region and far beyond.
He put the blame squarely on climate change.
“Every part of the country is getting hit by extreme weather,” Biden said in a briefing at the Somerset County emergency management training centre attended by federal, state and local officials, including New Jersey Governor Phil Murphy.
“We can’t turn it back very much, but we can prevent it from getting worse,” he said.
Hurricane Ida hit the gulf coast of Louisiana, August 29, as a powerful Category 4 storm, with sustained winds of 240km/h (150mph). It moved across the northeastern states, weakening into a post-tropical cyclone, dumping record rainfall on New York, New Jersey and Pennsylvania on September 1 and causing tornadoes.
Biden added that scientists have been warning of the dangers of climate change and that urgent action was needed.
“For decades, scientists have warned of extreme weather that would be more extreme and climate change was here,” he said, “and we’re living through it now, we don’t have any more time.”
Biden has approved major disaster declarations, making federal aid available for people in six New Jersey counties and five New York counties affected by the devastating floods.
Manville, situated along New Jersey’s Raritan River, is almost always hard-hit by major storms. It was the scene of catastrophic flooding in 1998 as the remnants of Tropical Storm Floyd swept over New Jersey. It also sustained serious flooding during the aftermath of Hurricane Irene in 2011 and Superstorm Sandy in 2012.
“I think the country has finally acknowledged the fact that global warming is real and it’s moving at an incredible pace and we have to do something about it,” Biden said.
“This is an opportunity,” he said.
At least 50 people were killed in six eastern states as record rainfall last week overwhelmed rivers and sewer systems. Some people were trapped in rapidly inundated basement apartments and cars, or were swept away as they tried to escape.
More than half of the deaths, 27, were recorded in New Jersey. In New York City, 13 people were killed, including 11 in the Queens neighbourhood.
New Jersey officials said four people are still missing.
Governor Murphy said on Tuesday it would take “months, more likely than weeks” to complete clean-up, repairs and rebuilding.
On the way to the briefing, Biden’s motorcade drove through a neighbourhood where piles of damaged furniture, mattresses and other household items were stacked outside homes.
Biden’s visit follows a Friday trip to Louisiana, where Hurricane Ida first made landfall, killing at least 13 people in the state and plunging New Orleans into darkness. Power is being slowly restored.
Earlier, White House spokeswoman Jen Psaki said Biden would emphasise that one out of three Americans lives in counties that have been impacted by severe weather events in recent months.
“The average costs of extreme weather are getting bigger, and no one is immune from climate change,” Psaki said.