Mr. Kimowitz’s two young daughters and his wife, Laura, were not home at the time of the attack, the authorities said.

The killings stunned residents of the leafy suburban town about 20 miles west of New York City. Until Saturday, there had been only 15 homicides in Maplewood, a town of about 25,000 people, over the past three decades, according to state and federal authorities.

Neighbors said on Sunday that they could hear Ms. Bermudez-Rodriguez screaming from inside their homes before she collapsed on the street.

“It’s a shocking feeling,” Kathy Cantwell, who lives next door to the Kimowitz family, said. “You wish you could have interceded or you could have saved David.”

Several neighbors said that in the days before the attack, they noticed a man they did not recognize sitting in a dark-colored sedan near the family’s house. While they had alerted one another about the man, they did not call the police. The authorities have not said whether that man was Mr. Porter.