A New Jersey woman is accused of fatally poisoning her husband’s 88-year-old grandmother with antifreeze.

The Gloucester County Prosecutor's Office said Mary Groatman was pronounced dead Thursday at Underwood-Memorial Hospital in Woodbury, four days after the alleged poisoning.

Anna Castagna, 43, of Brooklawn, N.J., is charged with two counts of murder and one count of aggravated assault, prosecutors say. She was being held on $250,000 bail.

Castagna's husband, Andrew Castagna, has not been named in the investigation, investigators say.

Castagna helped care for Groatman, who neighbors say lived for years in an upstairs bedroom at Castagna's home. The elderly woman recently fell down some stairs and had been taken to a rehabilitation center in Deptford, south of Philadelphia, neighbors told NBC10 reporters.

View NBC10Philadelphia.com's story on grandmothers' death by antifreeze

According to the Gloucester County Times, Castagna had apparently visited Groatman at the rehab site on Sunday,  the same day Groatman was discovered unconscious in her room.

"She was subsequently taken to the emergency room at Underwood-Memorial Hospital, where she underwent testing to determine the cause of her symptoms,” Gloucester County prosecutor Sean Dalton told the Gloucester County Times. “It was determined by the emergency room staff at Underwood-Memorial Hospital that she had ethylene glycol — the main ingredient in antifreeze — in her system.”

Dalton told NBC10 that Castagna had, in a time period leading up to the incident, "researched the effects of ingesting antifreeze on a human body." 

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"If it wasn't for the exhaustive and important work done by the emergency room, this lady might've gotten away with murder," Dalton told NBC10.

Dalton described Groatman as otherwise in good health for her age.

Neighbor Christine Priole told NBC10 that Castagna always took good care of Groatman.

"Whatever's going on, I just really don't think Anna would do something like that. And I stand behind her. I just can't fathom it! It's the craziest thing I've ever heard," Priole said.

NBC10Philadelphia.com's Karen Araiza and The Associated Press contributed to this report.

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