Police found the remains of 24-year-old Danvers High School math teacher Colleen Ritzer early Wednesday, Essex District Attorney Jonathan Blodgett said.
Her alleged killer, Philip Chism, was arraigned Wednesday in Salem on a murder charge and ordered held without bail. The teen is being charged as an adult.
Ritzer was reported missing late Tuesday night after she didn't come home from work or answer her cellphone. Investigators found blood inside a bathroom at the school and soon located her body, Blodgett said. He did not say how Ritzer died.
"She was a very, very respected, loved teacher," Blodgett said, calling the killing a "terrible tragedy."
The boy was also reported missing Tuesday after not coming home from school. Approximately one hour after blood was found in the bathroom, police found Chism and took him into custody.
Investigators said in court documents that the arrest was made based on statements by the suspect and corroborating evidence at multiple scenes. They said they also recovered video surveillance.
Ritzer's family released the following statement on Wednesday:
"At this time we are mourning the tragic death of our amazing, beautiful daughter and sister. Everyone that knew and loved Colleen knew of her passion for teaching and how she mentored each and everyone of her students. We would like to ask everyone to respect our privacy at this most difficult time."
Kyle Cahill, a junior, said he knows the teen suspect from the soccer team. He said Chism moved to Massachusetts from Tennessee before the school year began and played on the school's junior varsity soccer team.
He called him a quiet, nice kid.
"He wasn't violent at all. He was really the opposite of aggressive," Cahill said.
Authorities said there was no reason to believe anyone else was involved and there was no public safety danger. All public schools in Danvers were closed Wednesday.
ABC News and the Associated Press contributed to this report.