Dodge County authorities said on Wednesday that they will not file criminal charges in the suicide of a 13-year-old girl from Mantorville, Minn., late last month.

While investigators "believe that harassment and bullying were likely factors" contributing to the death of Rachel Ehmke, a seventh-grader at the Kasson/Mantorville Middle School, the county attorney determined there was "insufficient evidence" to prosecute anyone, the Sheriff's Office said in a statement.

"There is not one incident or action done by any particular student(s) that we believe is responsible," the statement said, adding that Ehmke "had problems with a number of different people, of different ages, over the past several months."

Ehmke died April 29 after hanging herself at her home. Authorities began investigating the circumstances surrounding her death after family and friends said that Ehmke, a popular girl who played several sports, had been a target of repeated bullying and name-calling at the school and online since the start of the 2011-12 school year.

Investigators said a nasty text message about Ehmke that was sent to several classmates days before her death to "get Rachel out of the school" originated from her father's house and was possibly sent by Ehmke herself. Because there was no suicide note, authorities said, "we can only speculate as to her motivation for sending this message out."

Authorities said Ehmke had been talking to friends and her family in the days before her death about transferring to another school because of the bullying.

The investigation remains open pending final autopsy results.

RICHARD MERYHEW