Irish teenager Phoebe Prince joined her Massachusetts school last autumn. Within six months, she had hanged herself in a cupboard, the victim of a "relentless" bullying campaign.

In the aftermath of her death, South Hadley High School has been forced to confront terrible questions about the way some of its children treated the newcomer.

The case, which has sent waves of dismay across the entire state and even nationally, centres on the misery suffered by Phoebe Prince, who was just 15 years old when she took her own life in January after what a prosecutor said had been months of bullying and taunting on school grounds, all arising, apparently, from her having dared briefly to date a school football player who was popular with other female students.

The abuse, which included the claim that the girl was an "Irish slut", were made both in person and in text messages on Facebook.

Massachusetts' Governor, Deval Patrick, said the charges, which could bring heavy sentences, were "a message that there will be consequences for this kind of behaviour. It's a terrible tragedy and all of us want to see consequences."

The death of Phoebe was among cases that spurred the state legislature in Boston to pass new anti-bullying laws earlier this month.

The district attorney who announced the charges, Betsey Scheibel, said Phoebe's death "followed a torturous day for her in which she was subjected to verbal harassment and threatened physical abuse".

Her tormentors threw a can at her as she walked home. Phoebe was later found hanging in a cupboard by her sister wearing the clothes she had worn to school.

The tormenting of the girl lasted for months, relentless almost from her first day at the school in South Hadley, a town in western Massachusetts where her family had settled after leaving Ireland last September. "The investigation revealed relentless activities directed toward Phoebe to make it impossible for her to stay at school. The bullying for her was intolerable," the attorney said.

One state legislator is calling for a new inquiry into the failures within the school common room. "I would hope the South Hadley school system would fully investigate and determine who knew what and when," said John W Scibak, a Democrat who represents the town.

"They should have put a stop to it," said Mitch Brouillard, who said that his own daughter had been attacked after speaking out against bullies at her school. He added that he was "appalled" that no action was being taken against staff members. An anti-bullying consultant, Barbara Coloroso, said she had advised the school on ways to identify and stamp out cases of harassment by students on fellow students long before the suicide of Phoebe and that her counsel had not been properly followed up.

For those who knew Phoebe, though, it comes too late. Not everyone at her new school loathed her: Sergio Loubriel (14) said that he had asked her to a winter dance with him, and regretted that he had never told her that he had a crush on her.

"I wish I could have stopped it," he said. "I wish I could have talked to her when she got home."