See more of the story

A onetime substitute teacher at a St. Paul charter school has been charged with criminal sexual conduct in an alleged classroom incident involving a 17-year-old student.

Caitlin K. Thao, 24, of St. Paul was charged in Ramsey County District Court last week with third-degree criminal sexual conduct. The incident allegedly happened at St. Paul City School this year.

A nationwide warrant has been issued for Thao's arrest. Messages were left with Thao seeking her response to the allegations. Court records do not list an attorney.

Eric Fergen, interim executive director for the charter school on University Avenue West, said Friday that Thao "hasn't worked with us for quite a few months." Fergen declined to comment further.

Fergen sent a letter to students' families and staff Friday disclosing the allegations and explained that the alleged encounter occurred after school hours.

According to the criminal complaint and a related court filing, a teenage boy told police on March 13 that the two had a sexual encounter about 1½ months earlier in an otherwise empty middle school classroom where Thao taught. Thao later invited the teen to her home but he declined, according to the court documents.

After Thao resigned in late February, she reported the sexual conduct to a social worker while in the Regions Hospital mental health unit, according to the court documents.