SAN ANTONIO -

A former Southside ISD middle school teacher is accused of sexually assaulting one of his students.

Raymond Casillas, 43, has been charged with aggravated sexual assault of a child.

According to an arrest warrant affidavit, the victim told San Antonio police Casillas sexually assaulted her in December 2011 at Julius L. Matthey Middle School when she was 13 years old.

The affidavit stated the victim told SAPD investigators Casillas invited her into his classroom during her lunch period, locked the door and cornered her in the room.

The victim claimed Casillas groped her and sexually assaulted her despite her pleas for him to stop, the affidavit stated.

The victim is now 15 years old and made the outcry during an interview at Child Safe on Dec. 23.

Casillas resigned soon after the alleged 2011 incident, said Southside ISD spokesman Jorge Popete.

Casillas has since been released from the Bexar County Jail on a $75,000 bond.

On Tuesday, a letter was sent home to parents. You can read that letter here.