Mackay had one more suggestion.  “The camera men, the extras, the technical and studio staffs—­they are not worthy of consideration, are they?”

Kennedy shook his head.

The odor of coffee struck my nostrils and I turned to find the percolator steaming.  Kennedy leaned over, to take a whiff.  Mackay rose.  At that moment there was a sudden crash and the window-pane was shattered.  Simultaneously a flash of light and a deafening explosion took place in the room, scattering broadcast tiny bits of glass from the laboratory table, splashing chemicals, many of them dangerous, over everything.

Kennedy hurried to the wreck of his paraphernalia.  In an instant he held up a tiny bit of jagged metal.

“An explosive bullet!” he exclaimed.  “An attempt to destroy my evidence!”

XXV

ITCHING SALVE

For once I rose with Kennedy.  He preceded me to the laboratory after breakfast, however, leaving me to wait for Mackay.  When the little district attorney arrived I noticed that he carried a package which looked as though it might contain a one-reel film can.

“The negative we took from the cameras at Tarrytown,” he explained.  “Also a print from each roll, ready to run.  I’ve been holding this as evidence.  Mr. Kennedy wanted me to bring it with me to-day.”

“He’s waiting for us at the laboratory,” I remarked.

“He’ll straighten everything up in a hurry, won’t he?”

“Kennedy’s the most high-handed individual I ever knew,” I laughed, “if he sees a chance of getting his man.”  Then I became enthusiastic.  “Often I’ve seen him gather a group of people in a room, perhaps without the faintest shred of legal right to do so, and there make the guilty person confess simply by marshaling the evidence, or maybe betray himself by some scientific device.  It’s wonderful, Mackay.”

“Do you think he plans something of that kind this morning?”

I led the way to the door.  “After what happened last night I know that Kennedy will resort to almost anything.”

The district attorney fingered the package under his arm.  “He might get everyone in the projection room then, and make them watch the actual photographic record of Stella’s death—­the scene where she scratched herself—­”

“Let’s hurry!” I interrupted.

When we entered the laboratory we found Kennedy vigorously fanning a towel which he had hung up to dry.  I recognized it as the one I had discovered in the studio washroom immediately following the first murder.

“This will serve me better as bait than as evidence,” he laughed.  “I have impregnated it with a colorless chemical which will cling to the fibers and enable me to identify the most infinitesimal trace of it.  We shall get up to the studio and start, well—­I guess you could call it fishing for the guilty man.”  He fingered the folds, then jerked the towel down and flung it to me.  “Here, Walter!  It’s dry enough.  Now I want you to rub the contents of that tiny can of grease, open before you there, into the cloth.”