A former teacher at Miss Porter's School has been charged with sexual assault for having sexual contact with a student at the girls' school. Joseph Prem Rajkumar, 42, was charged with two counts of second-degree sexual assault and one count of fourth-degree sexual assault. He was charged under the section of the law that makes it illegal for a school employee to engage in sexual conduct with a student. The warrant for Rajkumar's arrest is sealed and police declined to release much information because their investigation is continuing. Detectives took him into custody Monday afternoon and he was arraigned Tuesday in Superior Court in Hartford, where a judge set his bail at $500,000. He remains in custody.