The book presents a complex web of characters and red herrings, leading the reader to suspect various individuals. However, the evidence ultimately points to Mr. Bland as the person responsible for the murders.
Here's a summary of why:
* His motive: Mr. Bland is motivated by jealousy and a desire for revenge against the woman who had left him for another man, a man who happened to be the fiancé of one of the murder victims.
* His opportunity: Mr. Bland had access to the victims and the opportunity to carry out the murders. He even had a plausible alibi.
* His personality: Mr. Bland's odd behavior, his obsession with clocks, and his secretive nature all point to a disturbed individual capable of murder.
While Edna Brent is initially suspected, she is ultimately cleared as a suspect. Her connection to the murders is largely circumstantial and is later explained in a way that exonerates her.