Sarra Gilbert was “going through a lot right now,” her mother, Mari Gilbert, told a neighbor recently, and she asked him to “keep an eye out” for her, the neighbor said Sunday.

The neighbor, Ernest DeRosa, 33, a deli clerk, said he would see or hear Sarra Gilbert from time to time. He said he last saw her at an ATM a few blocks away from their building. She had her fists “clenched” he said, and she was hitting the ATM.

Sarra Gilbert, 27, has been charged with murder in the death of Mari Gilbert, 52, also the mother of Shannan Gilbert, whose body was found in 2010 near Gilgo Beach. The mother’s body was discovered Saturday in Sarra Gilbert’s apartment in upstate Ellenville.

DeRosa said he had few interactions with Sarra Gilbert.

“She would be home a lot, active, happy-go-lucky, you name it,” said DeRosa, who lives in an apartment adjacent to Sarra Gilbert’s. But sometimes, he added, she would stay in her apartment “or just disappear completely off the property.”

Loud arguing between Sarra Gilbert and her boyfriend could often be heard from the thin walls separating the units of the white clapboard, two-story house, he said, and he chose to mostly keep his distance from her.

Keith Moore has only lived next door to Sarra Gilbert for about two months, but said his stepmother and many others in this small upstate town knew the Gilbert family as they sought justice for Shannan Gilbert, and are reeling at Mari Gilbert’s death.

“The whole town is devastated,” said Moore, 32. “She was a sweet lady.”

The mothers and families of the victims found at Gilgo Beach formed a tight sisterhood, trading Facebook messages and showing up at events for one another, said Lorraine Ela, mother of victim Megan Waterman, who went missing a month and five days after Shannan Gilbert.

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The two met in 2010 when Gilbert attended an event for Waterman, Ela said.

“We hit it off right away. We both knew what each other were going through,” Ela, 49 of South Portland, Maine, said in a telephone interview Sunday. Gilbert went to all the half-dozen or so events Ela held for her daughter.

“She was caring, very outgoing. She loved her family and her grandchildren. You couldn’t ask for a better person,” she said. “It’s heartbreaking. I have no clue what happened, but Mari did not deserve to end this way.”

At the Walmart where Mari Gilbert worked in nearby Napanoch, co-workers expressed grief at the loss of the woman they described as hardworking and friendly.

Shannan Gilbert, 24, of Jersey City, center, disappeared in May 2010, near a remote stretch of Ocean Parkway. The search for her remains uncovered other human remains in the surrounding areas. Gilbert's remains were found in Oak Beach on Dec. 13, 2011. Photo Credit: Handout

Brett Barringer, who was collecting shopping cars in the parking lot, said she had worked at the store since 2013.

“I feel bad,” said Barringer, 25. “A lot, a lot of workers are going to miss her.”

Neighbor DeRosa said he developed a rapport with Mari Gilbert, who often showed up at her daughter’s apartment with groceries, cleaning supplies or to help care for her 3-year-old son.

They started to build a rapport, he said, and Mari Gilbert asked him to look after daughter Sarra.

“She said, ‘Just keep an eye out, make sure no one’s coming around bothering her. She’s going through a lot right now.’ She didn’t specify,” said DeRosa, who has lived in the building for about three years and said Sarra Gilbert lived there for about a year.

Mari Gilbert also confided in him about the loss of Shannan Gilbert, he said, though she didn’t go into great detail.

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“She said, ‘God took one of my children,’ ” DeRosa said. “She said it happened on the Island, and she just started choking up and couldn’t say anything more.”

With David M. Schwartz