In "The Catbird Seat," why didn't Mr. Martin kill Mrs. Barrows in her apartment?

Mr. Martin fully intended to kill Mrs. Barrows in her apartment. While she is mixing drinks in the kitchen, he looks all over for a suitable weapon. He considers several objects but decides that "None of them would do." Mrs. Barrows returns with the drinks before he has had a chance to find a weapon. 

"He had counted on finding one there." Up to that point he had seriously intended to commit the murder in...

Mr. Martin fully intended to kill Mrs. Barrows in her apartment. While she is mixing drinks in the kitchen, he looks all over for a suitable weapon. He considers several objects but decides that "None of them would do." Mrs. Barrows returns with the drinks before he has had a chance to find a weapon. 

"He had counted on finding one there." Up to that point he had seriously intended to commit the murder in her apartment. Then he changes his mind.

Mr. Martin, standing there with his gloves on, became acutely conscious of the fantasy he had wrought. Cigarettes in his pocket, a drink prepared for him--it was all too grossly improbable. It was more than that; it was impossible. Somewhere in the back of his mind a vague idea stirred, sprouted.

This is when Mr. Martin gets the inspiration to put on an act that will make Mrs. Barrows believe he is a heroin addict and a potential homicidal maniac. She believes him when he tells her he is preparing a bomb to blow up their boss. She becomes highly indignant and insists that Mr. Martin leave her apartment at once.

What follows is more effective than Mr. Martin could have planned. He doesn't have to commit a murder, and he gets rid of the vulgar woman who has been threatening to destroy his precious filing department. Mr. Fitweiler cannot believe her accusations when she goes into his office the next morning. He has known Mr. Martin for over twenty years and knows he doesn't drink or smoke. He certainly wouldn't be shooting up heroin! It is Mr. Martin who is in the catbird seat when it comes to a showdown with Ulgine Barrows. She loses her cool completely and calls their employer an old fool. She has to be dragged out of the office by two strong men, and that is the end of her days at F & S.