Martha Rendell appears to have first come to Perth in the early 1900s, following Thomas Morris, a man she had been having an affair with in Adelaide. In 1906, Morris and his wife Sarah Morris, violently quarrelled and he turned her out of the house. He moved in with Rendell and the five youngest of his nine children who were still living at home - Olive, Annie, George, Arthur and William, whose ages ranged from around 6 to 15. Mrs Morris did not try to contact her children after this time as they were thrashed if they spoke to her.
In April 1907, four of the children contracted diphtheria. All recovered, but Annie became ill again and died in July, with the puzzled family doctor concluding that her death was due to epilepsy and cardiac weakness. A few weeks later, Olive also took ill, dying after a few months. The doctor was again perplexed, but gave hemorrhage and cardiac weakness as the cause on the death certificate. In July 1908, Arthur began showing the same symptoms as Olive. He died in October, almost one year after his youngest sister. By now, doctors, suspicious of poisoning, conducted an autopsy, but were stopped halfway through by Rendell, who explained that she thought they had seen all they needed.
In April 1909, police found George at his mother's house, who had run away in fear for his life. William, the oldest of the five children, had made contact with his mother and taken George to see her. George refused to return to his father's house, causing Thomas to call the police to report his missing son. Shortly afterwards, Mrs Morris called the police as Thomas had stopped paying maintenance. When the police discovered George, he made allegations of poisoning which led to further investigations and promoted an exhumation of the three deceased children.
After the Coronial inquiry of Arthur Morris, Martha Rendell and Thomas Morris were committed to stand trial. Many incriminating testimonies were brought against Rendell, most concerning her swabbing the children's throats with 'spirits of salt' or hydrochloric acid, and she was found guilty whilst Morris was acquitted.
During Rendell's brief time in Prison, she spent much time in prayer and was visited by her spiritual adviser, Reverend Tom Allen, who harboured doubts as to her guilt. She protested her innocence all the way to her execution on the 6th of October 1909. Her last words before her death were "I will die brave", and a prayer for her two children she had left behind in South Australia. That day the female warders left the prison in tears.