The parents of Benjamin McLendon's 7-year-old victim got worried when they returned home to find the teen watching pornography.
Questions to their daughter about it late last year led to McLendon's Tuesday admission that he molested the girl.
McLendon, 17, pleaded guilty to child molestation before Superior Court Judge John Allen, who sentenced him to 10 years in prison, followed by 10 years' probation.
The sentence was an agreement between prosecutors and the defense.
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"I thought it was appropriate given all the circumstances," said Assistant District Attorney Don Kelly. "I discussed it with the family, and that was their wish as well."
McLendon, a relative of one of the parents, lived with them at their south Columbus home. The molestation had occurred for one or two months, but the parents didn't realize it until Dec. 29, when they found him watching the pornographic movie, Kelly said.
They questioned their daughter, who said she'd seen the movie and that McLendon had touched her. When interviewed at the Columbus Child Advocacy Center, she said even more, Kelly said.
"He realized he had done something wrong from the very beginning," said defense attorney Melvin Cooper.
Kelly said McLendon must register as a sex offender and obey restrictions once released, such as where he is allowed to live and that he have no contact with the victim's family.
Before being led from the courtroom by deputies, McLendon turned slightly toward the parents and softly spoke. "I apologize for my actions," he said before stepping away.