Fredric Brown (1906 – 1972) was an American writer of mystery, fantasy, and science fiction stories.

He was especially known for his short short stories with humorous or ironic endings. For example, “Dead Letter”, which appeared in Ellery Queen’s Mystery Magazine July 1955 page 65 as “The Letter”.

Blurb: Another detective-crime story complete on one page!
You can read it on the one page as it appeared in the magazine—

—or you can read it here:
DEAD LETTER
By Fredric BrownLaverty stepped through the open French windows and crossed the carpet silently until he stood behind the gray-haired man working at the desk. “Hello, Congressman,” he said.
Congressman Quinn turned his head and then rose shakily as he saw the revolver Laverty was pointing at him. “Laverty,” he said. “Don’t be a fool.”
Laverty grinned. “I told you I’d do this someday. I’ve waited four years. It’s safe now.”
“You won’t get away with it, Laverty. I left a letter, a letter to be delivered in case I’m ever killed.”
Laverty laughed. “You’re lying, Quinn. You couldn’t have written such a letter without incriminating yourself by telling my motive. Why, you wouldn’t want me tried and convicted—because the truth would come out, and it would blacken your name forever.”
Laverty pulled the trigger six times.
He went back to his car, drove over a bridge to rid himself of the murder weapon, then home to his apartment and to bed.
He slept peacefully until his doorbell rang. He slipped on a bathrobe, went to the door and opened it.
His heart stood still, and stayed that way.
The man who had rung Laverty’s doorbell had been surprised and shocked, but he had done the right thing. He had stepped over Laverty’s body into the apartment and had used the phone there to call police emergency. And he had waited.
Now, Laverty having been pronounced dead by the emergency squad, the man was being questioned by a lieutenant of police.
“Your name?” the lieutenant asked.
“Babcock. Henry Babcock. I had a letter to deliver to Mr. Laverty. This letter.”
The lieutenant took it, hesitated a moment, and then opened and unfolded it. “Why, it’s just a blank sheet of paper.”
“I don’t know about that, Lieutenant. My boss, Congressman Quinn, gave me that letter a long time ago. My orders were to deliver it to Laverty right away if anything unusual ever happened to Congressman Quinn. So when I heard on the radio—”
“Yes, I know. He was found murdered late this evening. What kind of work did you do for him?”
“Well, it was secret, but I don’t suppose the secret matters now. I used to take his place for unimportant speeches and meetings he wanted to avoid. You see, Lieutenant, I’m his double.”