CAMBRIDGE, Mass. — An association of black students at Harvard Law School says the university "woefully failed to act" after four students received offensive emails and text messages from an anonymous sender.

The Harvard Black Law Students Association issued a statement Friday criticizing the school after it was unable to determine who sent the "hateful, racist and sexist" messages, and after officials refused to share details of an investigation with students who received the messages.

Four students, including two who are black, notified school officials this year that they had separately received messages with comments including "we all hate u," ''you know you don't belong here" and "youre just here because of affirmative action."

Harvard officials say the case was investigated by university police, information technology officials and an outside law firm hired by the school, but they have been unable to determine who was behind the messages.

"Sadly, the realities of technology sometimes permit those who commit such acts to evade detection, and we are disappointed that we were unable to identify who is responsible despite our efforts along multiple fronts," a Harvard Law School spokesman said in a statement.

The student group believes the messages came from another student or students, but Harvard officials say that has not been confirmed. The group says the messages were sent from "retailer display phones" and two anonymous Gmail accounts.

Part of the dispute arises from a request to share details of Harvard's investigation. The four students say Harvard officials promised to provide the findings of the investigation but have refused to do so. Harvard officials say student privacy laws prohibit them from sharing the findings.

"For reasons of student privacy and confidentiality reflected in federal law and HLS practice, Harvard Law School will not publicly disclose details of investigations," Marcia Sells, the dean of students, said in a statement. "This practice is designed to protect the respective rights of all parties involved in any investigation."

Sells added that the school's administrators "continue to condemn in the strongest terms any communication or action that is intended to demean people." But the group says the four students relied on the administration's promise when they agreed to a school investigation.

"Now, more than seven months since the first hateful message was sent, the sender of this message remains unidentified and free to continue harassing Black and women students, meanwhile the targeted students have been left to continue fearing for their safety," the group said in its statement.

Simmering racial tensions have occasionally flared at the elite law school in recent years. In 2015, portraits of several black professors were vandalized in a Harvard Law building, with slashes of black tape placed over the photos. Harvard police eventually closed the case without finding a culprit.

Later, in 2016, the law school agreed to retire its official crest after students protested its connection to an 18th-century slaveholder, Isaac Royall Jr., who donated his estate to create the first law professorship at Harvard.