"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.