"The investigation revealed relentless activity directed toward Phoebe designed to humiliate her and to make it impossible for her to remain at school," District Attorney Elizabeth Scheibel said.
"The bullying, for her, became intolerable."
Students said Phoebe was called "Irish slut" and "whore" on Twitter, Craigslist, Facebook and Formspring.
Her books were routinely knocked out of her hands, items were flung at her, her face was scribbled out of photographs on the school walls, and threatening text messages were sent to her cell phone.
Scheibel said she had drawn the ire of the "Mean Girls" by briefly dating a popular senior football player in her first freshman weeks at the school. One student later said it felt like the whole school ganged up on her.
On Jan. 14, Phoebe was harassed and threatened in the school library and in a hallway, Scheibel said. As she walked home, one of the "Mean Girls" drove by and threw a can of Red Bull at her.
Phoebe walked into her house and hung herself in a stairwell.
The nastiness didn't even end there. Her tormentors posted vicious comments on the dead girl's Facebook memorial page.
For months, community anger simmered that no punishment had befallen Phoebe's bullies. Petitions were signed and town hall meetings held.
Scheibel said her investigators were taking the time to investigate thoroughly, and she slammed "the inexplicable lack of cooperation from Internet service providers, in particular Facebook and Craigslist."
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Phoebe Prince, South Hadley High School's 'new girl,' driven to suicide by teenage cyber bullies