Board Thread:Questions and Answers/@comment-918732-20160414155022/@comment-6331988-20161031001244

In The Sandman Vol. 2, at a Serial Killer convention, two Serial Killers are mentioned as being absent for unexplained reasons. Both of these Serial Killers had previously shown up in other DC/Vertigo Comics, where they died, explaining their absences. Who were these two Serial Killers?