Mary Ann Cotton was a Sunday-school teacher, a nurse, a Victorian wife and mother. Anybody would conclude that she was a hard-working woman struggling to look after her family in the most difficult of circumstances.

But in fact, she was the worst female serial killer in modern British history. Meet the real person behind two-part drama Dark Angel.

Who was Mary Ann Cotton?

It’s amazing that Cotton and her crimes aren’t better known, as it’s believed she murdered as many as 21 people. By the time she was hanged at Durham jail on 24 March 1873, aged 40, it’s thought she’d killed her mother, three of her husbands, a lover, eight of her children, seven stepchildren and a friend.

How did she murder so many people?

Using arsenic, the Victorian poisoner’s weapon of choice. It was easily available from the local chemist’s – to clean your house and get rid of bedbugs – and it was cheap, odourless and pretty much tasteless. You could slip it into tea or a stew and no one would know. Best of all, the body does not get rid of arsenic. It slowly builds up in the system, meaning that the patient murderer can administer it an ounce at a time and the slow deterioration of the victim’s health makes it look as if he or she is dying from a “natural” disease.

Alun Armstrong as George Stott and Joanne Froggatt as Mary Ann Cotton

There were certainly plenty of those around in the mid-1800s. In some very poor communities, infant mortality was as high as 50 per cent. The average life expectancy for men in the 1870s was just 41. Which explains why, certainly initially, no one noticed that wherever Cotton went, she was soon followed by death. Or that so many people close to her ended their days dehydrated and vomiting, clutching their chests in unbearable pain.

Numbed to the awfulness of unexplained illness, people would explain away death as “God’s way” or “part of the Lord’s plan”. 

How does Dark Angel depict this real-life killer?

Cotton’s story is told in a spellbinding new ITV drama, Dark Angel, made by World Productions, who gave us Line of Duty. The murderer – cool, clever, matter-of-fact – is played by Joanne Froggatt, best known as Downton Abbey’s Anna Bates. We see how Cotton starts hesitantly, becoming more brazen as her murder spree across the north east of England picks up speed. (As her lover gasps for breath, Cotton calls a neighbour to witness her holding him down.)

She moves from town to town – typically marrying a new man, having some children, before jettisoning them all – and goes on killing for two decades before being caught. Along the way, she often persuades her intended victim to take out life insurance. For this was a woman who was not merely a serial killer, she was also a bigamist, a forger, a fraudster and a thief.

How historically accurate is Dark Angel?

David Wilson, professor of criminology at Birmingham City University, was an adviser on the two-part drama, being the author of Mary Ann Cotton: Britain’s First Female Serial Killer. He says it wasn’t that difficult for a murderer – even a serial murderer – to go undetected in Victorian Britain. Particularly when your victims were young, as so many of Cotton’s were.

“She was a working-class woman and working-class kids died. A busy neighbourhood doctor wouldn’t think, ‘This is poisoning.’ And the other thing that helped her was that she regularly moved from place to place. She’d only need to move 15 miles and the people in the new place would have no connection with the village she’d just left.”

Better still, if you crossed from one police constabulary’s area to another. “There wasn’t much of a police force, and those forces which existed were incredibly local.”


What in Cotton’s life made her a murderer? Some people have suggested that she was influenced by the death of her father, in an industrial accident, when she was just nine. He’d fallen down a mineshaft and it’s said that his body was delivered back home, unannounced, wrapped in a sheet carrying the name of the mining company on it.

Wilson doesn’t give much credence to theories such as this. “How many of us have seen or had to deal with the death of a parent or a loved one? There’s a sense in which one telescopes backwards, trying to find the single cause that made her do what she did. But it can’t be put down to either nature or nurture, murderers ‘born’ or ‘made’. It’s a messy combination of things.”


That said, serial killing is often based on three things, says the criminologist: “Money. Power. Control.” He says that murderers can be divided into two camps, those who are “process-focused” and those who are “act-focused”. Cotton was clearly the former. “An act-focused killer kills suddenly, swiftly, immediately. The killer who is process-focused enjoys the time he or she can be with their victim, seeing their suffering.” Cotton’s decision to share the moment of her lover’s death with her neighbour places her firmly in the “process” category.

In a way, Cotton operated at the ideal historical moment for her crimes – in the brief window after the introduction of life insurance (it was just becoming mainstream), but before forensic science got going.

How was Mary Ann Cotton caught?

Cotton’s poisoning career finally came to an end when she became just a little too confident in her abilities to pick and choose who should live and who should die. At her trial, she protested her innocence. Charged with the death of her stepson Charles, Cotton admitted arsenic was present in the boy’s body, but claimed that she hadn’t put it there. Instead, he had breathed in noxious fumes from the green paint on the wallpaper at home. (In Victorian times, arsenic was everywhere – in wallpaper, curtains, toys, beauty products, even sometimes in beer.)


Wilson says: “But the amounts the boy had ingested were so huge you’d have had to munch the entire wall.” He is in absolutely no doubt about Mary Ann Cotton’s guilt – though no one can be certain of how many people she killed.

Neither does he doubt the enormity of her crime. He cannot think of any serial killer with a longer list of victims, apart from Harold Shipman a century later, who has been held responsible for more than 200 murders.

Nor was there any doubt about Cotton’s guilt among the Victorian public. Her case was taken up with glee by the newspapers, and, following her hanging, a chant became popular among children: “Mary Ann Cotton – she’s dead and she’s rotten.”

Those newspaper reports are instructive about public attitudes at the time. If you look at the drawings by courtroom artists, Mary Ann Cotton is depicted as a sinister, ugly figure. It is said that the artists were instructed to alter the defendant’s appearance to make her look like an old hag. In reality, she was an attractive woman in her late 30s. A woman of such evil intent needed to look the part.

“They monstered her,” says Wilson. “It was much easier for Victorian sensibility to think of her as not really a woman. She was a monster in human shape.”

Dark Angel airs on PBS Masterpiece on Sunday 21 May, 9/8c