The 84-year-old fled to the United States as a child, after Kristallnacht, the night of broken glass, in Germany.
It was a night when hundreds of Jews were killed.
Peter Chapman smashed a window and tried desperately to save his neighbor of 22 years.
"I was able to open the door. But, I looked. It was black smoke. I reached in. It was too hot. Obviously at that point I couldn't get in," Chapman said.
Firefighters found Charlotte Arner's body just a few feet away, at the front door of her Noel Drive home in the Village of Ossining.
Longtime neighbor Dede Emerson noticed smoke billowing out of the chimney bottom about 7:30 a.m.
"When you looked in, it was just black, like a curtain around the whole, I don't know how long the smoke had been in," Emerson said.
More than 60 Ossining firefighters poured water on the two-story stucco home until early Monday afternoon.
It's unclear where or how the fire started.
"The structure is made of block, stucco and shingles, the heat is retained inside. The fire could have burning an hour or so before anyone noticed smoke coming out," said Chief Thomas Reddy, of the Ossining Fire Department.
Charlotte Arner was 12 years old when she and her family fled Germany, just three days after receiving her passport in 1938.
Neighbors told Eyewitness News she was writing a book about her life.
Patty Chapman spent the last nine years helping Arner scan and document photos and mementos.
"This is a painting that is now in a museum in Berlin. It's Charlotte and her sister. This is little Charlotte. Here's Charlotte with her dad," Patty Chapman said.