Fritz von Weizsacker, the son of the late President Richard von Weizsacker, was stabbed to death on Tuesday while giving a lecture at a Berlin hospital, according to local police.

Authorities said a man stabbed von Weizsacker, 59, during his medical lecture at the Schlosspark hospital in the western Berlin neighborhood of Charlottenburg, where von Weizsacker is a senior internal medicine specialist. Police apprehended the attacker with the help of members of the crowd.

One other person, an off-duty police officer in the audience, was also seriously injured while trying to stop the attacker. The officer was taken to a different hospital to receive treatment, Berlin’s fire department said on Twitter.