Black tape was found over the pictures of black professors outside a Harvard Law School lecture hall Thursday, one day after students on the campus marched to express solidarity with black students at colleges across the country.

Campus police are investigating the matter, which was brought to light after a law student shared the image on Twitter.

"I am saddened and angered by this act," Martha Minow, a dean, wrote in an email to students. She was meeting with students at the school to discuss the incident, The Boston Globe reported.

The paper reported that the tape was eventually removed and replaced with positive comments about the professors.

Dozens of students gathered in the Science Center Plaza at about 3:30 p.m. Wednesday to support black activists on other college campuses.

The Harvard Crimson reported that the protesters were joined by administrators, including Harvard President Drew G. Faust.

"I think we've got a lot of work to do," Faust said after the protest, according to the Crimson, "and I look forward to working with the community of students and others to make sure everybody at Harvard feels included."