Three Omaha middle school students have been expelled amid shocking allegations, accused of sexually assaulting a fellow student at school last week.

The day after Channel 6 News first reported alleged incidents of sexual assault at McMillan Magnet School, principal Dan Bartels responded to the allegations, saying the incident was unfortunate and regrettable.

However, the mother of the alleged 13-year-old victim spoke exclusively with Channel 6 News, saying she wanted answers as to why something like this happened.

Principal Bartels responded, “It was inappropriate, it was unwanted, it was taken too far by young people, absolutely."

Bartels showed where the alleged sexual assault took place last Monday between the three boys and the girl. He explained that it happened during a 20-minute transition period between classes and after students were done practicing in the main auditorium for a spring concert.

According to the school’s investigation, Bartels said only one incident of the alleged assault took place. The girl’s mother, who Channel 6 News is not identifying to protect her daughter’s identity, says she believes another incident happened the next night while the students waited to perform during the concert.

The victim’s mother said Monday, "Again, they were grabbing her and touching her and holding her up against the wall, there was no supervision."

"We, as of today, do not have evidence to say something inappropriately happened on Tuesday," said Bartels . "I'm not saying that it didn't, but I am saying that I have facts that say it happened on Monday."

The mother insisted there was a lack of supervision. However, Bartels said it was not whether a teacher was present, but what a teacher did or did not see. “Did staff monitor the class, she (teacher) was there, she was monitoring the class, but she did not inform because she was not aware of anything inappropriate that occurred?”

Bartels tells Channel 6 News that once the mother reported the situation on Friday, the school immediately launched an investigation. The district enforced the school's code of conduct that same day. Police did cite the boys with misdemeanor sexual assault and they were released to their parents.