A Blaine teacher charged with second-degree criminal sexual conduct in connection with the alleged molestation of one of his fourth-grade students has been the focus of an earlier investigation that did not result in charges.

Johnsville Elementary teacher Kenneth L. Sonnenfeld Jr., 52, of Oak Grove, was released from jail on Thursday after he posted bail, which was set at $100,000. He is on administrative leave from the Anoka-Hennepin School District after he was charged with molesting a 10-year-old girl five or six times from December 2014 to the end of May 2015.

According to the complaint filed this week, the girl told sheriff's investigators that she was molested several times last year. In one instance, her teacher touched her under her underclothing as he helped her with her school work as she stood next to his desk while class was in session, she said.

Similar allegations were made against Sonnenfeld in 1997 by two students in his fourth-grade class at Lincoln Elementary School in Anoka. No charges were filed, because the county attorney's office said they couldn't be proven beyond a reasonable doubt.

According to a memorandum explaining the case and why no charges were filed, two girls in Sonnenfeld's class told investigators in separate interviews that he had inappropriately touched them over and under their clothing while in the classroom. The memo from the county attorney's office states that there was no corroborating evidence and that a jury would have had to have been convinced of the facts based solely on the two students' testimony.

A jury would have had "great difficulty" believing the teacher inappropriately touched the students in the classroom on numerous occasions without other students seeing it, the memo states. The students' motives and credibility likely would be challenged, the memo said.

The School District's investigation into that case didn't result in discipline, according to spokesman Jim Skelly. District officials said they can't release details because of data privacy policies.

Sonnenfeld, who was put on administrative leave in May 1997 during that investigation, returned to teaching that fall but in a fifth-grade classroom at Andover Elementary School, according to district records. Skelly said there's no paperwork that indicates whether it was Sonnenfeld's choice or a district request that he teach at a different school.

After Sonnenfeld was charged earlier this week in the Johnsville Elementary case, a student who had been in his class eight years ago came forward to complain about her former teacher's classroom behavior that had made her feel uncomfortable. She didn't report any physical contact, sheriff's officials said. The conduct didn't constitute criminal behavior, so authorities said no further investigation is warranted.

Sonnenfeld has been with the district as a teacher for the past 24 years, Skelly said.

Mary Lynn Smith • 612-673-4788