A professor at Columbia University’s Teachers College who was propelled into the national spotlight when a noose was found on her office door last fall has been found to have plagiarized the work of a former colleague and two former students, the college has announced.

The college, in statements to the faculty and the news media, said an 18-month investigation into charges against the professor, Madonna G. Constantine, had determined there were “numerous instances in which she used others’ work without attribution in papers she published in academic journals over the past five years.”

Susan H. Fuhrman, the college’s president, and Thomas James, the provost, informed the faculty of the case, and said that Dr. Constantine had the right to appeal.

The college said Dr. Constantine was being penalized, but did not say what the penalty was. A spokeswoman for the college, Marcia Horowitz, said Teachers College did not have set rules governing plagiarism or how it should be punished.