WINTER HAVEN, Fla. (AP) — Two Florida girls who were primarily responsible for bullying a 12-year-old girl who killed herself were arrested after one of them acknowledged the harassment online, a sheriff said Tuesday.

Police in central Florida have been investigating the death of 12-year-old Rebecca Sedwick, who climbed a tower at an abandoned concrete plant Sept. 9 and hurled herself to her death. Authorities said as many as 15 girls may have bullied Rebecca and the investigation was continuing.

Polk County Sheriff Grady Judd said the arrests of the girls, ages 14 and 12, were hastened when the older girl posted Saturday on Facebook, saying she bullied Rebecca but she didn't care.

"We decided that we can't leave her out there. Who else is she going to torment, who else is she going to harass?" Judd said.

The 14-year-old girl was accused of threatening to beat up Rebecca while they were sixth-graders at Crystal Lake Middle School, telling her "to drink bleach and die" and saying she should kill herself, the sheriff said. The older girl convinced the younger girl to bully Rebecca, and they both repeatedly intimidated her, called her names and once the younger girl even beat Rebecca up, police said.

Both girls were charged as juveniles with third-degree felony aggravated stalking. If convicted, it's not clear how much time, if any at all, the girls would spend in juvenile detention because they did not have any previous criminal history, the sheriff said.

"Time may not be the best trainer here. We've got the change this behavior of these children," Judd said.

The sheriff's office identified the two girls, but The Associated Press generally does not name juveniles charged with crimes.

Judd said the bullying began after the 14-year-old girl started dating a boy Rebecca had been seeing. The older girl didn't like that and "began to harass and ultimately torment Rebecca," Judd said.

A man who answered the phone at the 14-year-old's Lakeland home said he was her father and told The Associated Press "none of it's true."

"My daughter's a good girl and I'm 100 percent sure that whatever they're saying about my daughter is not true," he said.

At the mobile home, a barking pit bull stood guard and no one came outside despite shouts from reporters for an interview.

Neighbor George Colom said he had never interacted personally with girl but noticed her playing roughly with other children on the street.

"Kids getting beat up, kids crying," Colom said. "The kids hang loose unsupervised all the time."

A message left at the 12-year-old girl's home was not immediately returned.

The girls were arrested Monday night and released to their parents' custody. Judd said the 14-year-old was "very cold, had no emotion at all upon her arrest."

The girls remain on home detention.

The younger girl was Rebecca's former best friend, but the sheriff said the older girl turned her and others against Rebecca, out of fear they would be bullied, too.

Before her death, Rebecca changed one of her online screen names to "That Dead Girl" and she messaged a boy in North Carolina: "I'm jumping." Detectives found some of her diaries at her home, and she talked of how depressed she was about the situation.

Last December, Rebecca was hospitalized for three days after cutting her wrists because of what she said was bullying, according to the sheriff. Later, after Rebecca complained that she had been pushed in the hallway and that another girl wanted to fight her, Rebecca's mother began home-schooling her in Lakeland, a city of about 100,000 midway between Tampa and Orlando, Judd said.

This fall, Rebecca started at a new school, Lawton Chiles Middle Academy, but the bullying continued online, authorities said.

Judd said he was upset the girls who were arrested still had access to social networks, even after Rebecca's suicide.

"If we can find any charges we can bring against their parents, we will," Judd said.

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