DANVERS, Mass. (AP) — A police officer has been stationed today outside a high school in Danvers, Mass. -- part of the extra security in place today as students returned for the first time since a classmate allegedly killed a teacher earlier this week.

The body of the teacher, Colleen Ritzer, was found in the woods behind the school. The 14-year-old suspect is charged with murder.

At the school today, the U.S. flag flew at half staff, and pink ribbons hung from a row of trees. An electronic sign displayed a tweet that Ritzer had posted this summer. It said, "Being good to people is a wonderful legacy to leave behind."

Written on the windows of a pickup truck in the student parking lot, in the school colors of blue and white, were the words, "RIP Miss Ritzer. Gone, not forgotten."

One student who was in one of Ritzer's classes said this morning, "We can get through it, but it's really not going to be the same."

This afternoon, officials at Assumption College, where Ritzer graduated in 2011, held a memorial service in her honor. The Rev. Dennis Gallagher, who officiated at the service about 50 miles from Danvers, said Ritzer's death left behind "a mountain of sadness."

Authorities have offered no clues on any motive for the killing.