NORTHAMPTON, Mass. – Insults and threats followed 15-year-old Phoebe Prince almost from her first day at South Hadley High School, targeting the Irish immigrant in the halls, library and in vicious cell phone text messages.

Phoebe, ostracized for having a brief relationship with a popular boy, reached her breaking point and hanged herself after one particularly hellish day in January — a day that, according to officials, included being hounded with slurs and pelted with a beverage container as she walked home from school.

Now, nine teenagers face charges in what a prosecutor called “unrelenting” bullying, including two teen boys charged with statutory rape and a clique of girls charged with stalking, criminal harassment and violating Phoebe’s civil rights.

School officials won’t be charged, even though authorities say they knew about the bullying and that Phoebe’s mother brought her concerns to at least two of them.

Northwestern District Attorney Elizabeth Scheibel, who announced the charges Monday, said the events before Phoebe’s death on Jan. 14 were “the culmination of a nearly three-month campaign of verbally assaultive behavior and threats of physical harm” widely known among the student body.

“The investigation revealed relentless activity directed toward Phoebe, designed to humiliate her and to make it impossible for her to remain at school,” Scheibel said. “The bullying, for her, became intolerable.”

Scheibel said the case is still under investigation and that one other person could be charged. It wasn’t immediately known Monday whether the teens who have been charged have attorneys.

Scheibel said the harassment began in September, occurring primarily in school and in person, although some of it surfaced on Facebook and in other electronic forms. At least four students and two faculty members intervened to try to stop it or report it to administrators, she said.

Schiebel refused to discuss the circumstances of the rape charges.

No school officials are being charged because they had “a lack of understanding of harassment associated with teen dating relationships,” and the school’s code of conduct was interpreted and enforced in an “inconsistent” way, Scheibel said.

“Nevertheless, the actions — or inactions — of some adults at the school are troublesome,” she said.

A message seeking comment was left Monday for South Hadley Schools Superintendent Gus A. Sayer.

Phoebe was born in Bedford, England and moved to County Clare, Ireland, when she was 2. She moved last summer to South Hadley, home to Mount Holyoke College, because the family had relatives there.

Her family has since moved away and could not immediately be located for comment. Scheibel spoke for them at a news conference to announce the charges.

“The Prince family has asked that the public refrain from vigilantism in favor of allowing the judicial system an opportunity to provide a measure of justice for Phoebe,” she said.

Some students accused of participating in the bullying have been disciplined by the school and will not be returning to classes.

The Massachusetts Legislature cited Prince’s death and the apparent suicide of 11-year-old Carl Walker-Hoover of Springfield last year when members passed anti-bullying legislation earlier this month.

South Hadley is among several college towns in western Massachusetts that pride themselves on their urbane cultural offerings, good schools and safe streets. After Phoebe’s death, the community formed an anti-bullying task force that drew more than 400 people to its first meeting in February.

Robert Judge, a South Hadley selectman and task force member, said hundreds of people have become involved in hope that something good comes from the incident.

“Like most towns, we like to think of ourselves as a good place to live, and then this happens and your reputation is sullied nationally and even internationally, and people look at you differently, and they make assumptions,” Judge said.