HOUSTON --The parents of students at a Houston ISD high school are getting an important letter from the principal. It details a crime one a former employee is accused of committing. The incident is alleged to have happened off camp last summer. When the fall semester began, rumors of the encounter were investigated by HISD police. Now, two felony charges have been filed. Until last November at Madison High School, there was a 20-year-old clerk who worked at the school office. Her name is April Castillo and students say they remember her still. "There'd be a lot of male students in there than females -- like she let them stay there instead of telling them to go to class or give them a pass, and I was like, 'OK, it was kinda weird,'" student Cina Dennis said. Last summer though, according to a probable cause document, Castillo gave two 15-year-old male Madison students a ride in her car. That, according to police, turned into a sexual encounter in the back seat with one of the students. Castillo, according to the document, admitted to it. She was fired, and on Friday, a letter was sent home with students. "Allegations that an office clerk may have had an inappropriate relationship with a student were made in late November," Madison High School Principal Sonja Williams wrote. "An investigation was immediately launched by campus police and administrators. We notified Child Protective Services and the Houston Police Department, which launched its own investigation." "As a result of our investigation, the clerk was terminated on January 5, 2011," the statement continued." Castillo may be gone from school, but she's not forgotten. "It's not surprising because sometimes, there'd be a whole lotta male guys and she would just close the door and let them stay," said Dennis. According to court documents, Castillo is charged with improper relationship with a student and sexual assault of a child. Bond on each charge has been set at $30,000.