A group of 15 teenage girls is reportedly under investigation in connection with the suicide of a 12-year-old former classmate, the Lakeland Ledger reported on Thursday.

Polk County Sheriff Grady Judd said at a press conference Thursday that Rebecca Ann Sedwick had been "absolutely terrorized on social media" for more than a year before killing herself. Her body was found early Tuesday morning at a former cement plant. Sedwick was reported missing Monday night after she failed to come home from school.

Judd also said that Sedwick shared her plan to commit suicide with an online friend, identified as a 12-year-old boy living in North Carolina. Sedwick reportedly told the boy, "I'm jumping, I can't take it anymore" and changed her screenname on a phone-messaging program, Kik Messenger, to "That Dead Girl."

WTSP-TV reported on Wednesday that Sedwick's family said at a vigil that officials at Crystal Lake Middle School, where the bullying against her began, did not respond when they filed a report. But after transferring her to another school and deleting her Facebook page, the abuse reportedly continued online, on sites like Instagram and Ask.fm.

"We've lost a beautiful child that had a bright future. For what reason? To be bullied?" a man identified as Sedwick's uncle told the crowd of mourners. "Why? 'Cause your clothes are better than hers? Your shoes look better than hers?"

Judd said on Thursday that the parents of the 15 girls identified in the investigation are cooperating with his department, and that several cell phones and laptops have been confiscated.

Watch WTSP's report from the vigil, aired Wednesday, below.