“Do you suppose it was used because it was quick and was colorless, so as not to be noticed in the glass?” I hazarded.

Kennedy paced up and down the laboratory several times in thought.  “To me, Walter, this is another indication of the satanic cleverness of the unknown criminal in the case.  First Miss Lamar is to be killed.  For that purpose something was sought, probably, which could not be traced easily to the perpetrator.  In snake venom an agent was employed which may be said to be almost ideal for the grim business of murder.  It is extremely difficult to identify in its results, it is comparatively unknown, yet it is swift in action and to be obtained with fair ease.

“Differing from most poisons, it may be inflicted through a prick so slight as to be almost unnoticed by the victim.  The scheme of fixing the needle in the curtain was so simple and yet so effective that the guilty person need never have feared its discovery under ordinary circumstances, or its association with the girl’s death, if some one stumbled upon it accidentally.  The idea of returning for the death-dealing point was only one of the many details of a precautionary measure upon which we have stumbled.  Had I found it the next morning I would have been unable, in all probability, to identify it as belonging to or as obtained by any of our suspects.

“You must realize, Walter, that with all the scientific aids I have been able to bring to bear we possess almost no direct evidence.  There are no fingerprints, no cigarette stubs, no array of personal, intimate clues of any sort to this criminal.  These are the threads which lead the detective to his quarry in fiction and on the stage.  Here we lack even the faintest description of the man, or woman if that is her sex.  It is murder from a distance, planned with almost meticulous care, executed coolly and without feeling or scruple.

“After the death of Miss Lamar I was not so sure but that the selection of the snake venom was simply the inspiration of a perverted brain, the evolution of the detailed method of killing her—­an outgrowth of someone’s familiarity with studio life in general, with the script of ‘The Black Terror’ in particular.  Now I realize that we are face to face with the studied handiwork of a skilled criminal.  These two deaths may be his—­or her—­first departure into the realm of crime.  But potentially we have a super-villain.

“I make that statement because of the manner of Werner’s demise.  It is evident that the director stumbled on a clue to the murderer.  If my first hypothesis had been correct, if the use of snake venom and the unlucky thirteenth scene had been largely a matter of blind chance in the selection of poison and method, then we might have expected Werner to be struck down in some dark street, or perhaps decoyed to his death—­at the best, inoculated with the same crotalin which had killed Miss Lamar.