(CNN) -- A Massachusetts grand jury Thursday indicted 14-year-old Philip Chism on charges of murder, aggravated rape and armed robbery in connection with last month's slaying of his algebra teacher, Colleen Ritzer, according to the Essex district attorney.
Citing Massachusetts law, prosecutors said they would ask that Chism be tried in an adult court.
"The indictments ... detail horrific and unspeakable acts," said District Attorney Jonathan Blodgett.
The armed robbery indictment alleges that Chism, armed with a box cutter, robbed Ritzer of credit cards, an iPhone and her underwear. The aggravated rape indictment alleges that he sexually assaulted her with an object.
Under the aggravated rape and armed robbery indictments, Chism was charged as a youthful offender, but prosecutors said they will move to join those charges with the murder case in Superior Court.
"This is the first step in a long process to secure justice for Ms. Ritzer and her family," Blodgett said.
Ritzer was known to her friends and family as a woman who inspired many, whether it be in the classroom or online, with her heart, intellect and positive spirit.
"She was happy," said Jen Berger, Ritzer's best friend. "I don't even know what the world is like without her. It's a scary thought."
A 2011 graduate of Assumption College who was working toward a master's degree at Salem State University, Ritzer seemed to always wear a wide smile and was approachable to students and colleagues alike, said Charlotte Dzerkacz, who became good friends with Ritzer in 2011 when they taught at the same middle school.
"She was energetic, she was compassionate," Dzerkacz said. "You couldn't ask for anything more from a teacher or a friend."
In a statement, the Ritzer family said: "We are devastated and heartbroken by the details of the horrific circumstances surrounding the death of our beautiful daughter and sister, Colleen."
Chism allegedly killed Ritzer, 24, on October 22 in the girl's bathroom of Danvers High School with a box cutter he brought to school, a source close to the investigation told CNN.
Ritzer went to a regular girls bathroom on the second floor when someone was using the locked faculty bathroom.
Chism followed her in, according to the source. Ritzer was punched a few times before being killed, officials said.
Her body went into a recycling bin, then outside the school where it was tossed, the source said. Authorities found a bin that apparently had been thrown off an embankment some 100 feet away from Ritzer's body.
After changing his clothes, Chism went to a Wendy's restaurant and a movie, according to the source.
Denise Regan, Chism's public defender, declined to comment.
A week after the slaying, about 400 Danvers High School students were among the estimated 1,000 people who gathered to pay final respects at the church where the family of popular math teacher worshiped.
Many mourners wore pink clothing -- Ritzer's favorite color -- and pink flowers decorated the outside of Andover's St. Augustine Church.
The Rev. Peter G. Gori, in his homily, offered advice on how to approach Ritzer's death. "Perhaps we should ask not why, or even how she died, but rather why and how did she live," Gori said.
Authorities are still investigating the motive for her killing.
Documents filed in a Tennessee court 12 years ago may shed light on Chism's past.
The court papers showed that Chism's father agreed during a separation from his mother to have restricted time with his son, who was then 2, because of "prior physical and emotional abuse as well as alcohol abuse." The documents said the parents were attempting to reconcile.
Chism's uncle, Terrence Chism Blaine, told CNN in the days after the crime that the boy's parents are now separated and that the father -- a former military man -- now lives in Florida.
The suspect's mother, Diana Chism, last month released a statement through her son's attorney saying her "heart is broken for the Ritzer family and the loss of their daughter and sister Colleen Ritzer."
"Her son was born in love and is dear to her, very dear," the statement said.
CNN's Alexandra Field, Rande Iaboni, Pamela Brown, Don Lemon and Greg Botelho contributed to this report.