A former Indian Trail Academy security guard convicted of sexually assaulting a student must spend 10 years in prison, a judge decided Thursday.

John R. Clark, 47, also must register as a sex offender for the rest of his life and have 10 years supervision once he is released from prison.

During that time, Kenosha County Circuit Judge Wilbur W. Warren III said, Clark may not contact his victim or her family.

“I’m very, very, very sorry about this. This is my fault. I take responsibility,” Clark said and wept. “...I will have to live with myself for what I have done. Parents and students trusted me. I let them all down.”

Clark, who got credit for nearly 16 months already served, pleaded guilty in September to child enticement and second-degree sexual assault of a child. He faced 40 years in prison.

The victim’s father said no sentence could have been harsh enough for a man who not only violated his then 15-year-old daughter, but also violated the public trust through his position as a school security guard.

“He took a girl who trusted him and physically and sexually abused her, then threatened her family,” the father said. “...He has taken a part of our daughter that can never be replaced.”

The girl, now 16, said she is sickened by flashbacks of her contact with Clark and has been called a “liar” by classmates reluctant to believe her allegations.

“Now everyone knows me as the girl who was sexually assaulted by John Clark,” she said.

The girl said she considered suicide as the criminal case went on and was hospitalized.

Ultimately, she chose to live and try to learn to deal with the trauma of the assaults.

“If I take my life, he would end up winning,” she said.

Defense attorney Loren Keating echoed Clark’s willingness to take responsibility, explaining that Clark did not do so sooner because he could not “get past” assertions that he had threatened the girl with violence; Clark was adamant that no threats were made, Keating said.

Clark was charged in September 2008.

He was accused of assaulting the girl, who was 15 at the time, outside of school five times between April and May 2008.

He also reportedly threatened to kill the student’s family and a friend if she told anyone about their sexual contact.

The abuses reportedly started after the girl added Clark as a friend on the social networking Web site MySpace “as a kind of joke,” the criminal complaint indicates.

Clark reportedly sent the girl provocative messages, whispered in her ear and put snacks in her locker.

It apparently was not the first time Clark had crossed the line with a student, prosecutor Michael Graveley said.

In 2007, another female student reported that Clark had been sexually inappropriate in speaking and dealing with her.

Clark was disciplined in January 2008 and ordered not to talk to female students, Graveley said.

Within three months, the contact with the 15-year-old student began.

Keating cited a history of mental illness, which included electroshock therapy, as well as Clark’s history of drug and alcohol abuse and classification as a “slow learner” as a child in explaining Clark’s mindset.

The personal history did not excuse Clark’s behavior, but helped explain how Clark “left his own body, left his own personality” and crossed the line with a student, Keating said.