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.

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.

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.

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