As the news of Rex Heuermann’s arrest in the Gilgo Beach murders rippled through his Long Island neighborhood, shock gave way to questions about another person in the rundown red house.
“I guess people don’t expect a serial killer to be married,” said Frankie Musto, who lives two houses away from Mr. Heuermann in Massapequa Park, a bedroom community an hour from Midtown Manhattan.
Ms. Musto was standing on her porch, discussing with family and neighbors how a man a police official described as “a demon that walks among us” could remain married for years.
During the years that investigators say Mr. Heuermann was preying on young women, he lived in the red house with his wife, Asa Ellerup, 59, and their two children.
Mr. Heuermann was charged Friday with three counts of first-degree murder; he is also the prime suspect in the death of a fourth woman. His lawyer says Mr. Heuermann, who was held without bail, denies committing the killings, and wept after his arrest.
His wife has not been charged and investigators said she was out of state or out of the country when all the killings happened. Investigators say stray strands of her hair helped link her husband to the bodies, which were found in 2010.
Questions about Ms. Ellerup rippled along the bustling checkout counters on Monday morning in the IGA supermarket where she shopped several times a week for more than 20 years.
“Could he have been a monster who killed those girls and an angel at home?” said Mery Salmeri, a store manager. “Or maybe his family was just so scared of him that they were like his prisoners who would never tell anyone, even if they had some idea of what he was capable of.”
Cashiers at the supermarket knew them as a quiet, cheerless family that shopped several times a week. Ms. Salmeri said she watched their children grow up over the past 25 years. One thing remained constant, she said: Mr. Heuermann never accompanied them.
“He never came with them,” she said. “I’m not sure what that says about them.”
Ms. Ellerup looked depressed, Ms. Salmeri said, and the family often paid with food stamps, unusual at this store.
Prosecutors say Mr. Heuermann’s use of disposable burner phones — to contact his victims, to keep tabs on the investigation and to access cruel pornography — not only helped him elude the authorities for years, but may have kept his wife in the dark.
Criminologists say serial killers can be married and seem well adjusted. And, said Scott Bonn, a criminologist and researcher, “It’s not unusual for the wives and families of serial killers to be completely unaware about their darker compulsions.”
“They’re able to compartmentalize,” he said, “and see no contradiction in being a caring parent and partner in one aspect of their lives and in another, torturing and killing people,” he added.
The family’s location following Mr. Heuermann’s arrest was unclear. They were not seen this weekend as crime scene workers carried a succession of evidence boxes out of the house into trucks, or on Monday when the authorities searched a storage unit in nearby Amityville.
Both the accused man and his wife have spent their lives in the commuter suburbs of New York. Ms. Ellerup grew up about two miles from Mr. Heuermann after she and her sister emigrated from Iceland with their parents. Her mother is deceased, neighbors said, and her father still lives in the family’s house. He did not answer the door on Monday.
Ms. Ellerup attended Farmingdale High School and married briefly in her 20s and was divorced in the early 1990s in Queens. It was unclear whether she had a professional life outside the home.
On Ms. Ellerup’s apparent Twitter account, which had not been active in a decade, she posted about her passion for comic book conventions and taking vacations and vented about cold weather. Her handle, @ElvenMaiden, was an apparent reference to a video game.
The Mustos, like other neighbors, called Mr. Heuermann’s family reclusive and enigmatic. On a tight-knit block, they did not socialize. Their unkempt house stood out almost as an extension of their nature.
To Ms. Musto, Ms. Ellerup did not seem concerned with appearances either. “It could be middle of the afternoon and she looked like she just rolled out of bed,” she said.
“I’m friendly with everybody around here but she didn’t talk to anyone,” Ms. Musto said.
There was speculation but little insight into Mr. Heuermann’s relationship with his wife and his family life. Their closest neighbors said they did not know them well and not one neighbor recalled anyone outside the family ever being allowed — or wanting to go — inside the house.
The couple’s son’s name remained unclear. Their daughter, Victoria, 26, worked with Mr. Heuermann at his Manhattan firm.
Ms. Musto’s daughter, Taylor, 27, said she grew up and played with Victoria as a child.
“She was always quiet. She would ask me to come over,” Taylor Musto said. This did not sit well with Taylor’s mother.
“I didn’t want her in that house,” Frankie Musto said.
“It could be that he just had two personalities,” said her husband, Bob Musto, a 40-year resident.
According to the authorities, Mr. Heuermann took pains to hide his activity from his wife.
When one victim, Megan Waterman, was reported missing in June 2010, Ms. Ellerup was in Maryland, the authorities said. She was in New Jersey in September 2010 when Amber Lynn Costello vanished, and in Iceland in July 2009 when Melissa Barthelemy was last seen.
Some serial killers are able to keep their secret “the same way some men are able to have a second family on the side and no one knows,” said James Alan Fox, a professor at Northeastern University who has been studying serial killers for more than 40 years. “It’s something they do in their own free time, and how would the family know?”
Hurubie Meko and Erin Nolan contributed reporting.