(CBS News) Investigators say bullying drove Rebecca Sedwick to take her own life and believe as many as 15 girls were involved in a relentless campaign of harassment.
Two of those girls, a 14-year-old and a 12-year-old,, a third degree felony.
Authorities said they arrested these two suspects now because of something one of them posted online over the weekend.
Polk County Sheriff Grady Judd told CBS News' Anna Werner that what these two girls' did to Sedwick was criminal because "they terrorized her."
"They did things like, 'You should die, you should drink bleach and die," said Judd. "You see a pattern of harassment, a pattern of intimidation and that's what they did. They intimidated this girl. They harassed her. She had no peace."
Judd said investigators were also troubled by something the older girl posted on social media on Saturday.
"She made a comment in reference to, 'Yeah I bullied Rebecca, and yeah she's dead, but I don't give a blank,'" he said. "I met with the detectives and supervisors yesterday afternoon and said, 'She needs to go to jail. We need to arrest her.'"
Police said the girls' parents refused to cooperate and both girls were arrested Monday at their homes.
Sedwick's mother, Tricia Norman, said that her birthday would have been Saturday and this is a "huge birthday present for her."
Last December Sedwick cut her wrists and then last month she climbed an abandoned tower in a concrete plant and.
Court papers allege the older girl began harassing Sedwick after she started dating Sedwick's former boyfriend. The affidavits filed by a police investigator also indicate the younger girl and Sedwick were once close friends, but that the 14-year-old may have convinced the younger girl to turn on Sedwick, even getting her to beat up her former best friend.
Judd said that this type of behavior should not happen and parents should be aware of what their children are doing.
"It only can happen when parents don't parent their children," he said. "You need to know what they're talking about online. You need to know who their friends are. You need to know if they're bullying people at school."