Patricia Wentworth 
The Blind Side [EPUB ebook] 

Ross Craddock's killer must have felt quite at home. There was Lee Fenton, Ross's cousin, heard calling Ross "a swine" before sleepwalking (so she claimed) into the victim's flat. The spinster aunt, whom Ross was evicting, that just happened to see a figure fleeing the house. And there was the blood-smudged Mavis Grey; and Bobby Foster, Mavis's suitor with fingerprints everywhere. With so many clues and suspects throwing themselves at Inspector Lamb, how could he possibly notice the deadliest one of all?