"She Was in Three Places Miles Apart at One and the Same Time"

"Invisible Death."
By Anthony Pelcher (1897-1981).
First appearance: Astounding Stories, January 1930.
Included in Anthology of Sci-Fi, V16, The Pulp Writers (2013).
Novelette (22 pages).
Online at Project Gutenberg HERE.

"On Lees' quick and clever action depended the life of 'Old Perk' Ferguson, the millionaire manufacturer threatened by the uncanny, invisible killer."

Darius Darrow, an eminent mechanical engineer, has died—but definitely not of natural causes; someone, it seems, wants to make an example of his death and use it as leverage in an extortion plot that could net them millions, as this charming billet doux from the killer indicates:

Old Perk: Get wise to yourself. We are in a position to destroy you and all the pot-bellies in the Wall Street crowd. If you want to die of old age, remember what happened to Darrow and begin declaring us in on Wall Street dividends. If you do not you will follow Darrow in the same way.

Our first demand is for $100,000. Leave this amount in hundreds and fifties in the rubbish can at the corner of 50th Street and Broadway at 10 A. M. next Thursday. If you fail we will break your damned neck. Bring the police with you if you like. — Invisible Death.

Principal characters:
~ Mrs. Susan Darrow, "one of the world's foremost chemists", widow of Darius Darrow: "He was working on an invention that he said would do away with war and would make the owner of the device a practical world dictator, should he choose to exercise such power. The device was completed. The murderer killed him to secure his device. That all seems plain enough."
~ Peck, the gardener: "The auto started itself, and what is more, that auto only went about a hundred yards when it disappeared altogether—like that—like a flash."
~ Perkins Ferguson ("Old Perk"), head of the Schefert Engineering Corporation, who pays royalties on some of the Darrow patents: "I have my own theory, however, but I am going to know a whole lot more about this case before I venture it."
~ Damon Farnsworth, first V. P. of Schefert Engineering: "The Darrow case has taken a sudden and sinister turn."
~ Walter Lees, a young engineer who doubles as our sleuth: "For the first time in my life I am going to be a Peeping Tom."
~ Adolph Jouret ("Elias, the Great"), retired magician: "When you find your man, you will find a madman."
~ Doris Jouret, Adolph's daughter: "The girl had adopted rather a theatrical pose, which disclosed considerable of her nether charms, and said nothing at all."

Typo: "a coal chute. This shoot . . ."

Comments: Engineers tend to be methodical and not given to flashes of inspiration, which our "detective" Walter Lees amply demonstrates.

Resources:
- There's practically nothing about Anthony Pelcher lying about on the Internet; both the ISFDb HERE and FictionMags HERE indicate a small output, with only five SF/Fantasy titles from this author.

The bottom line: "To do such a thing would be to transcend magic. And I beheld, unclouded by doubt, a magnificent vision of all that invisibility might mean to a man—the mystery, the power, the freedom. Drawbacks I saw none. You have only to think! And I, a shabby, poverty-struck, hemmed-in demonstrator, teaching fools in a provincial college, might suddenly become—this.” 
― Griffin