Police are investigating as a possible hate crime a threatening letter sent to the principal of Canarsie High School that contained a noose.

It was the fourth noose incident reported in the city in less than a month, police said. They have said they are concerned that copycats might be imitating a noose incident that fueled a recent racial conflict between white and black high school students in Jena, La. The police had not received a complaint of a noose in the city for more than five years before this month. Yesterday, the Brooklyn principal, Tyona Washington, who is African-American, received a letter that contained derogatory comments about blacks and said she didn’t deserve to be principal, police said.

The letter was signed with the name of a white administrator at the school, but police said they believed that the letter had been sent by someone else. The envelope also contained multicolored cotton cloth that had been tied into the noose, and the letter suggested the principal use it to hang herself.

Police were called immediately, according to Department of Education officials. The noose and letter were sent to the police crime laboratory in Queens for analysis.