CHICAGO (CBS) — A suburban mental health center is being sued by the parents of a 13-year-old girl. They blame the institution for the sexual assault of their daughter.

In April, 18-year-old Cody Pomrenke and the girl were both living at Northern Illinois Academy in suburban Aurora.

The lawsuit says while on a field trip to the Aurora Public Library, Pomrenke lured the girl into a men’s bathroom and assaulted her.

The girl’s father says the school should never have left them unsupervised, because Pomrenke had a history of sexual aggression they knew about, which included grooming the young girl ahead of the trip.