PHILADELPHIA (CBS)– A high school teacher in Allentown is suspended after he’s accused of sexually assaulting a student.

Christopher Johnson, 34, turned himself in to police on Thursday.

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The investigation began when parents of the victim looked at their daughter’s cell phone and noticed there were inappropriate communications between their daughter and Johnson.

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Officers say Johnson had a sexual relationship with a student after he started tutoring her earlier this year. Police haven’t said how old the girl is.

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Johnson has been suspended from his job at Parkland High School.