It was particularly alarming, the district attorney said, that some teachers, administrators and other staff members at the school were aware of the harassment but did not stop it. “The actions or inactions of some adults at the school were troublesome,” Ms. Scheibel said, but did not violate any laws.

Christine Swelko, assistant superintendent for South Hadley Public Schools, said school officials planned to meet with the district attorney this week or next. “We will then review this evidence and particularly the new information which the district attorney’s office has but did not come to light within the investigation conducted by the school,” Ms. Swelko said in a statement.

Ms. Prince’s family had recently moved to the United States from a small town in Ireland, and she entered South Hadley last fall. The taunting started when she had a brief relationship with a popular senior boy; some students reportedly called her an “Irish slut,” knocked books out of her hands and sent her threatening text messages, day after day.

At South Hadley High School, which has about 700 students, most students and teachers refused on Monday to talk about the case. Students waited for parents in the pouring rain and a sports team ran by, with one student telling reporters, “Go away.”

Ashlee Dunn, a 16-year-old sophomore, said she had not known Ms. Prince personally but had heard stories spread about her in the hallways.

“She was new and she was from a different country, and she didn’t really know the school very well,” Ms. Dunn said. “I think that’s probably one reason why they chose Phoebe.”

Image South Hadley High School in western Massachusetts. Credit... Christopher Capozziello for The New York Times

On Jan. 14, the investigation found, students abused her in the school library, the lunchroom and the hallways and threw a canned drink at her as she walked home. Her sister found her hanging from a stairwell at home, still in her school clothes, at 4:30 p.m.