(CNN) A black lawmaker who resigned in Vermont "was a victim of racial harassment," the state's attorney general said, but the case won't be prosecuted because of the First Amendment.

In an announcement Monday, Attorney General T.J. Donovan said former state Rep. Kiah Morris had been subjected to speech that was "clearly racist and extremely offensive," but the perpetrator, a self-confessed white nationalist, cannot be sanctioned because of protections of free speech.

Morris and her husband began receiving anonymous messages, including racist tweets, in March 2016, according to the attorney general's findings. The harassment continued for months and involved instances of online harassment, theft and vandalism. The Bennington Police Department and Vermont State Police launched investigations. In August 2018, the Attorney General's Office launched an independent investigation that resulted in Monday's decision not to seek prosecution.

"Kiah and her family were victims of crime," Donovan said in a news conference on Monday , adding that "the harassment was often based on Kiah Morris' race and gender" and carried out "in a context of vicious racial harassment."

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