Blood found in a second-floor school bathroom helped lead investigators to the body of Colleen Ritzer, a 24-year-old math teacher at Danvers High School who was reported missing when she didn't come home from work on Tuesday, Essex District Attorney Jonathan Blodgett said.
"She was a very, very respected, loved teacher," Blodgett said.
The suspect, Philip Chism, was arraigned on a murder charge Wednesday and ordered held without bail. The teenager, described by classmates as soft-spoken and pleasant, also did not come home from school the day before and was spotted walking along Route 1 in the neighboring town of Topsfield at about 12:30 a.m. Wednesday.
Officials didn't release a cause of death and haven't discussed a motive in the killing.
A court filing said Ritzer and Chism were known to each other from the high school, but it did not elaborate. The arrest was made based on statements by the suspect and corroborating evidence at multiple scenes, investigators said in court documents.
Ritzer's family said they are 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 provided by her uncle Dale Webster.
At his arraignment in adult court in Salem, Chism's defense attorney argued for the proceeding to be closed and her client to be allowed to stay hidden because of his age. The judge denied the request. The lawyer, Denise Regan, declined to comment outside court. No statement had been released from his family by Wednesday evening.
The tall, lanky teenager had moved to Massachusetts from Tennessee before the start of the school year and was a top scorer on the school's junior varsity soccer team, said Kyle Cahill, a junior who also plays soccer. He said the team had been wondering where Chism was when he skipped a team dinner Tuesday night.
"We're all just a family. It just amazes me really," Cahill said. "He wasn't violent at all. He was really the opposite of aggressive."
Ritzer had a Twitter account where she gave homework assignments, encouraged students and described herself as a "math teacher often too excited about the topics I'm teaching."
She was a 2011 graduate of Assumption College in Worcester, a school spokeswoman said Wednesday. She graduated magna cum laude with a bachelor of arts degree in math, a minor in psychology and a secondary education concentration, according to the college's 2011 commencement program.
One of her former students, Chris Weimert, 17, said she was a warm, welcoming person who would stand outside her classroom and say hello to students she didn't teach. He said she had been at the school for two years.
"She was the nicest teacher anyone could ever have. She always had a warm smile on her face," he said.
Ryan Kelleher, a senior, said students related to the young teacher, who liked to wear jeans and UGG boots just like the teenagers she taught. Kelleher, who also plays soccer, said the arrest of the soft-spoken Chism didn't make sense to him.
"From what I know about him and seeing him every day, it just doesn't add up that he would do such a thing, unless this was all an act to fool somebody," the 17-year-old said.
Ritzer lived at home with her 20-year-old brother and her sister, a high school senior. The close-knit family was often outside, barbecuing, spending time together and enjoying each other's company, neighbors said.
Mary Duffy has lived next door to the Ritzers in the suburban neighborhood in Andover since the family moved there more than two decades ago. She had known Colleen Ritzer from the time she was a baby and said the Ritzers' oldest child had just one life ambition: to be a high school math teacher.
"All I ever heard is that she loved her job," Duffy said.
All public schools in Danvers, about 20 miles north of Boston, were closed Wednesday.
Hundreds turned out for a candlelight vigil Wednesday evening on the parking lot of the school. Many wore pink, Ritzer's favorite color. They prayed and sang and, at the end of the vigil, they placed their candles along with some stuffed animals in the middle of a ring they have formed for the gathering.
"She supported all of us. We should be there to support her," said Danvers senior Courtney Arnoldy, 18, who had Ritzer for a teacher.
Ritzer is the second teacher allegedly killed by a student in the U.S. this week. A Sparks, Nev., middle school teacher was allegedly shot by a 12-year-old student on Monday.
Associated Press writer Lynne Tuohy in Andover and news researcher Rhonda Shafner in New York City contributed to this report.