A person known to the French authorities as a radical Islamist with mental health troubles stabbed a German tourist to death and wounded two people in central Paris on Saturday before being arrested, officials said. The attacker was known to authorities as a radical Islamist and was being treated for mental illness, Interior Minister Gerald Darmanin said at the scene by the River Seine,adding that the man had shouted "Allahu Akbar" ("God is greatest") before being arrested.