Patricia Ward was found dead in the street at around 8 p.m. Tuesday. A knife was recovered in the apartment, police said.
Dale Silverman, a medical editor who lives in the same Long Island community, was driving away from the train station shortly before police arrived.
"I saw what I thought was a head in the street. I saw long, black, straight hair and the head face down," she said Wednesday. "And I did a double-take. And I opened the window and said, 'No, that can't be what that is.'"
"I saw the body, completely straight legs together, hands at its side," said Silverman, pointing to still-bloodstained areas of the street several yards apart.
"It looked fake," she said. "I thought it was a stupid Halloween prank."
Another witness, Nick Gordon, told Newsday he saw a trail of blood on the apartment building stairs.
Derek Ward was arrested years ago for gun possession and criminal mischief and had a psychiatric history going back about 10 years.
Patricia Ward, who taught language arts in a program that prepares high school students for college, "was a member of the campus for 28 years," Farmingdale State College said in a statement. "She was well-known, well-liked and well-respected. The campus is a very sad place today."
The body was found near a home decorated with Halloween pumpkins, fake cobwebs and a mock graveyard.
"At first, everyone thought it was like a Halloween prank," said neighbor Barbara Smalls, recalling Wednesday morning how she had seen the sheet-covered body. She also "thought maybe it was a mob hit or something."
"This doesn't happen here," said Smalls. "This is a very nice, nice neighborhood. People are very friendly."