VAUGHAN, Ont. — Police north of Toronto say a 28-year-old woman who worked as an occasional supply teacher is facing sexual assault charges. York regional police say they began investigating late last month after receiving information about a teacher who is alleged to have been involved in a sexual relationship with a male student between October and December of last year. They say Marianna Riossi has been working with the York Catholic District School Board since 2014. The 28-year-old woman from Vaughan, Ont., has been charged with three counts of sexual assault and three counts of sexual exploitation.