Anthony Berkeley

A woman thinks her husband may be planning to kill her. (imdb)

Dr. Edmund Bickleigh is married to a particularly overbearing woman who reminds him at every turn that he is living in her house. But the doctor has outside interests to help him cope: many of the town's female population seems to have had intimate relations with him. When a new arrival to town becomes involved romantically with Edmund, he decides maybe it was time his wife wasn't around much longer. He puts in place a plan to murder his wife and stop whoever gets in his way (imdb)

After philosophy Professor Todhunter is told he has 6 months left to live, he is barred from teaching by his college so there won't be a scandal if he drops dead in class. Discussing a hypothetical man with 6 months to live with a group of friends, Todhunter asks each what he'd do in his last 6 months. One says he'd commit a "social murder", that is kill someone who's not a criminal but without whom society would be better off. The professor starts to obsess about this idea.