Professor David Guth has been placed on leave because of a tweet he published after this week's mass shooting in Washington, the University of Kansas said Friday, Sept. 20, 2013. Guth tweeted "blood is on the hands of the #NRA. Next time, let it be YOUR sons and daughters." (AP Photo/University of Kansas, Chuck France)

Professor David Guth has been placed on leave because of a tweet he published after this week's mass shooting in Washington, the University of Kansas said Friday, Sept. 20, 2013. Guth tweeted "blood is on the hands of the #NRA. Next time, let it be YOUR sons and daughters." (AP Photo/University of Kansas, Chuck France)