In and then there was none who is suspected of miss Brent death?

In Agatha Christie's "And Then There Were None," the character suspected of Miss Emily Brent's death is Dr. Edward Armstrong. He is accused of having caused her demise by administering a lethal dose of poison, reflecting the overarching theme of justice and retribution in the novel, as each character confronts their past crimes in a setting where they cannot escape their fate.