(CNN) -

A Massachusetts high school student accused of raping and killing his math teacher has been indicted on charges he attacked an employee at a youth services facility, a district attorney's office announced Wednesday.

According to the Suffolk County District Attorney's office, on June 2, Philip Chism followed a 29-year-old female employee into the bathroom at the Metro Youth Services facility in the Boston neighborhood of Dorchester and physically assaulted her.

"Co-workers heard her cries for help and interrupted the assault," the district attorney's office said.

On Wednesday, Chism, 15, was charged with attempted murder by strangulation, assault with intent to murder, kidnapping and two counts of assault and battery with a dangerous weapon.

Chism remains in custody. Suffolk County Juvenile Court has not set an arraignment date for these charges. His lawyers didn't answer calls from CNN when the new allegation surfaced last month.

The teenager is accused of killing his algebra teacher, 24-year-old Colleen Ritzer, last October at Danvers High School, about 20 miles north of Boston. Police and prosecutors say he used a box cutter to kill Ritzer in a girls' bathroom.

Chism pleaded not guilty to aggravated rape, robbery and murder charges in January. He is being tried as an adult.