Victorian serial killer Mary Ann Cotton is thought to have claimed the lives of up to 21 people with her arsenic-filled teapot, and yet she was convicted of just one crime: the murder of her young stepson, Charles Edward Cotton.

So how did this come to be? 

ITV/PBS Masterpiece drama Dark Angel tells the story of nine of her murders, ending in (historical spoiler alert) Mary Ann facing the hangman’s noose. The drama is based on the book Mary Ann Cotton: Britain's First Female Serial Killer by historian David Wilson and remains true to many of the details of how the poisoner got found out – but there is much more to the story between the arrest and the hanging.

Here’s what really happened… 

How did she attract suspicion?

Dark Angel sees Mary Ann practically give herself away when she tells local druggist Mr Riley that she will soon be rid of her orphaned stepson, who stands in the way of her re-marriage: “The Cottons are not a long-lived family.”

Unreal as it may seem, this actually happened: for whatever reason, Mary Ann – perhaps emboldened by getting away with murder for so long – hinted to Riley that Charles Edward's days were numbed. Soon the boy was dead.

Suspicious? Undoubtedly. Local doctor Dr Kilburn did a post-mortem of the boy’s body on Mary Ann’s kitchen table, but he ran out of time before the coroner's inquest and suggested it was probably gastroenteritis. Mary Ann was triumphant – and Charles Edward was buried.

But the story didn’t end there, just as it didn’t in the drama: The unhappy druggist badgered Dr Kilburn to look again at the contents of the boy’s stomach which had been preserved in a jar, and when he did, he found arsenic. Mary Ann was arrested.

An early report came in the North Wales Chronicle: "A FEARFUL SUSPICION. – Mary Ann Cotton, a widow, is in custody at West Auckland, charged with having poisoned her stepson, aged eight years. It is said that the prisoner, who is comparatively a young woman, has had three husbands and 15 children, and that they, as well as two lodgers, died under her roof." More was to come out.

A (perhaps deliberately) unflattering portrait of Mary Ann Cotton

What about the other murders? 

Mary Ann is suspected to have murdered many more of those close to her, including eleven of her children, her mother, her best friend and three of her four husbands.

As all the gory details came out, there was plenty of insinuation in the newspapers about Mary Ann's long and death-filled life story as the pieces all fell together. 

The Illustrated Police News reported that many close to her “are said to have died under somewhat suspicious circumstances.” 

The Penny Illustrated Paper and Illustrated Times wrote that Mary Ann was “suspected of further poisonings” and, referring to James Robinson, added: “She had tried to get this, her third, husband to insure his life; but this he persistently refused. Of four husbands she has had he is the only survivor.”

The lucky James Robinson in Dark Angel

The Home Office soon gave permission for the exhumations of the bodies of Mary Ann’s lover Joseph Nattress, her stepson Frederick Cotton Jnr and son Robert Robson Cotton.

After Joe's body was dug up, the Evening Gazette reported on 16th September 1872: “Although five months have elapsed since the internment, the body was in a fair state of preservation… There was nothing, in the opinion of the medical gentlemen present, to account for death from natural causes.” The Standard added: “They found unmistakable symptoms of poison.”

Why was she only convicted of one murder?

While Mary Ann was only convicted of one murder, she actually had two magistrate’s court hearings. 

The first was about the death of Charles Edward, in August 1872; the second, after a break so Mary Ann could have her final baby within the confines of Duham Gaol, took place in February 1873 and concerned Joe, Frederick and Robert Robson. 

This second hearing never went any further, as Mary Ann was tried and convicted at a Crown court for the murder of Charles Edward Cotton on 7th March 1873. 

Joanne Froggatt as Mary Ann Cotton in Dark Angel

What happened at the trial? 

Mary Ann kept steadfastly silent at her trial, but she made it known in her letters that she maintained her innocence.

In one, she wrote: “I hope you Will not Juge me rong As i have been on the Awfill crime of murder of Charles Edward Cotton Whitch i am not guilty of it those to reade the evidence that come sin against me you may think i am but ifie must Tell you I am not guilty I have been miss Lead.” 

Her court-appointed QC tried to argue that Charles Edward’s death was the result of accidental ingestion of arsenic from wallpaper. But as Wilson told the Radio Times, "The amounts the boy had ingested were so huge you’d have had to munch the entire wall.” 

Significantly, the judge allowed prosecutor Charles Russell to refer to medical evidence about the poisonings of Joe Nattress and the two other exhumed bodies. The jury unanimously found Mary Ann guilty after just an hour of deliberation.

How did she die?

The Lloyd’s Weekly Newspaper reported: “While the wretched woman harbours a strong conviction that the royal clemency will be extended towards her, she staunchly asserts her innocence of the crime she has been convicted of.”

The paper also reveals sympathy for her plight in giving up the young baby for adoption by her former neighbours: “The parting of the wretched mother with her child was a very affecting one.”

 The Dundee Courier & Argus added: “During the last few days the cold, reserved manner which has been apparent in her demeanour ever since her examination before the magistrates, has somewhat given way, and she is now realizing the awful position in which she is placed.”

Mary Ann was hanged on March 24th 1873, watched by 20 reporters.

One Dundee Courier journalist wrote: “Mrs Cotton, who scowled fiercely and with an air of defiance at the crowd, and who muttered constantly but indistinctly, took her place upon the drop with remarkable composure… the wretched woman was launched into eternity.” 

The only refreshment she took before her death? A cup of tea.