The Supreme Court on Thursday said recordings of a teacher obtained by parents through a device hidden in their child's backpack cannot be used as evidence in a criminal child abuse case.

The Supreme Court has overturned a original ruling that handed down a fine of 5 million won ($3,800) to an elementary school teacher for violating the Child Abuse Punishment Act, sending the case back to Seoul Eastern District Court.

The teacher, whose identity has not been disclosed, was accused of emotionally harassing a third-grade student who transferred to the class by saying things like, "You look like a child who hasn't been to school," "I want to open (the student's) brain up," "What is that fool raising (his/her) hand for, (the student) doesn't even know what (the answer) is."

The evidential value of the recording was a pivotal issue in the case. The teacher's statements were recorded through a taping device the student's parents had hidden in the child's backpack in order to substantiate the child's claims of being emotionally abused.

In the first trial, the teacher was sentenced to six months in prison and two years of probation. The teacher was also ordered to complete 40 hours of child abuse rehabilitation.

The second trial, which was held following the defendant's appeal, found the accused guilty of 14 of the 16 statements they were accused of making, and fined the teacher 5 million won. The defendant argued that the recorded evidence had no evidentiary value because it was collected secretly or illegally. This argument was not accepted by the appellate court.

However, in the Supreme Court's review of the appeal, the court determined that the recordings should be denied evidential value under the Protection of Communications Secrets Act, which stipulates that no person shall record or listen to a conversation between others that is not open to the public. The act also states that the contents of telecommunications recorded by illegal means cannot be used as evidence in trials or disciplinary proceedings.

"The defendant's remarks in class, which were secretly recorded by the parents of the child, are classed as 'undisclosed conversations' and 'conversations between others,'" explained the Supreme Court. The teacher's remarks were only disclosed to students in the classroom, and as the parents were not directly involved in the conversation, the recording has no evidential value.