The Boston Globe reports that school CCTV cameras showed the accused pushing a recycling bin through the building. It is assumed (but not verified) that Ritzer's body was inside. She was found dead in woods behind the school, after being reported missing late on Tuesday. Authorities believe that Chism went to a matinee showing of the new Woody Allen movie, "Blue Jasmine," shortly after murdering Ritzer.
Officials said Ritzer and the suspect knew each other from the school, but did not elaborate.
Gardner Trask, chairman of the Danvers Board of Selectmen, told the Associated Press news agency the killing is a "devastating blow" to the close-knit town. Danvers High School, in a suburb of Boston, reopened on Thursday for students to speak to counsellors. Classes will resume on Friday.
On Wednesday evening the Boston Red Sox held a moment of silence for Ritzer before the first game of the World Series. And hundreds of people attended a candlelit vigil in the school's parking lot, wearing pink clothing or bows in tribute to Ritzer's favourite colour.
Ritzer reportedly lived in her family home with her younger brother and sister. Her family said they were mourning the death of their "amazing, beautiful daughter and sister".
"Everyone that knew and loved Colleen knew of her passion for teaching and how she mentored each and every one of her students," the family said in a statement.
Ritzer was said to be friendly towards the school's students, many of whom were not much younger than her.
Her Twitter biography describes the math teacher as "often too excited about the topics I'm teaching". She used the account to set homework for students. The suspect's family and lawyer have not spoken to reporters.
The accused had moved to Massachusetts from the state of Tennessee before the start of the school year. He was said to be a star player on the school soccer team. One student, Kyle Cahill, told the Associated Press the suspect's absence had been noted at a team dinner on Tuesday night.
"We're all just a family. It just amazes me really," said Kyle. "He wasn't violent at all. He was really the opposite of aggressive."
Other students said they were absolutely shocked that Chism could have killed the popular educator
Ritzer's death is the latest incident this week to send police scrambling to a US school:
- On Wednesday an 11-year-old in the north-western state of Washington was charged with attempted murder after bringing 400 rounds of ammunition, a handgun and several knives to his school
- A teacher was killed on Tuesday in Sparks, Nevada, by a 12-year-old boy who then turned the firearm on himself. Two other students were wounded in the shooting