PHILADELPHIA (AP) — A Drexel University professor has been put on leave after his tweets suggested a link between white supremacy and the massacre at a Las Vegas music festival.

Associate professor George Ciccariello-Maher wrote in an op-ed piece published Tuesday by The Washington Post that the college placed him on leave after a series of tweets about the shooting prompted death threats.

Last week, Ciccariello-Maher, who teaches political science and global studies, posted a tweet that read “It’s the white supremacist patriarchy, stupid” followed by a series of similar statements. He wrote in the op-ed that threats came in after conservative media outlets highlighted his tweets.

Drexel says that the decision was necessary to ensure the safety of the campus.

Ciccariello-Maher did not respond to an emailed request for additional comment.