Being easily led, and as keen on making money as Seddon was himself, Barrow was quickly persuaded by Seddon to sign over to him a controlling interest in all her savings and annuities, including £1,500 of India Stock, in return for which he would take care of her for the rest of her life, giving her a small annuity and allowing her to live in his home rent free.

She improved slightly for a few days, but was confined to her bed where, on 13 September, she made a will, dictated to and executed by Seddon, and witnessed by his relatives.

[8] Seddon went to the doctor, who issued a death certificate without seeing the body, claiming that he was unable to attend due to overwork brought on by an epidemic current in the area at that time.

[5] Barrow's cousin, Frank Vonderahe, suspicious over the suddenness of the death and how quickly the funeral arrangements had been made, arrived to take over possession of her estate.

However, Seddon informed him that nothing was left as he had paid the substantial funeral expenses and the cost of Ernest Grant's upkeep himself.

Barrow's body was exhumed on 15 November 1911, and an examination of it by Sir William Willicox, the senior Home Office specialist, and young pathologist Bernard Spilsbury, who had already made a name for himself in the Crippen case, discovered about two grains of arsenic.

[10] As in the Crippen trial, Spilsbury showed himself to be an outstanding witness for the prosecution, easily dealing with cross-examination by the junior defence barrister and demonstrating highly effective forensic techniques.

During their trial at the Old Bailey the prosecution, led by the Attorney General, Sir Rufus Isaacs KC,[5] proved that Margaret Seddon had previously bought a large amount of flypaper, which contained arsenic.

Despite the advice given by his Counsel, Seddon insisted on giving evidence in his own defence;[12] it was claimed that he turned the jury against himself through his arrogant and condescending attitude.

Certainly, his case was not helped by his ridiculous claim that Barrow might have drunk water from the dishes of flypaper that had been placed in her room to keep away the flies.

A former Freemason,[4] on being asked by the Clerk of the Court if he had anything to say as to why the sentence of death should not be passed against him, Seddon replied at length and appealed directly to the judge, Sir Thomas Townsend Bucknill, as a brother Mason and in the name of 'The Great Architect Of The Universe' to overturn the jury's guilty verdict.

Bernard Spilsbury, who went on to become a famous pathologist and who gave evidence during the trial, was not yet involved in Freemasonry,[14] and so the meaning of what had passed between Seddon and Bucknill was lost on him at the time.

[19] The case was reevaluated using modern forensic techniques in an episode of the BBC series Murder, Mystery and My Family (2020) which reinvestigated the evidence against Seddon.