The fourth installment of the Netflix show has landed, following on from Jeffrey Dahmer, the Menendez brothers and Ed Gein. Now, Monster is turning its attention to its first female subject in a case that’s so famous, it’s got its own nursery rhyme…

“Lizzie Borden took an axe, and gave her mother 40 whacks. When she saw what she had done, she gave her father 41.”

The rhyme is, for the most part, inaccurate, but it gives you an idea. Nearly 135 years ago, Lizzie’s father and stepmother (not her mother), Andrew and Abby Borden, were brutally killed at their home in Fall River, Massachusetts, with a hatchet (not an axe).

Suspicion soon fell on Lizzie, who was at home around the time of the murders and gave conflicting accounts of her movements. She was eventually charged and tried for both killings, but with no evidence conclusively linking her to the crime, she was acquitted – and no one else was ever charged.

While this crime is at the centre of Monster, with Ella Beatty taking on the titular role, the case has been given a Murphy makeover by making her relationship with Bridget “Maggie” Sullivan (Vicky Krieps) – the Bordens’ live-in maid – a major part of the plot.

“When the repressed daughter of a wealthy New England family and her rebellious maid find themselves trapped in a house built on humiliation and cruelty, they escape into a fantasy of sex, power, and revenge,” the synopsis reads.

With that in mind, you’re no doubt wondering how true to life their relationship is.

Was Lizzie Borden sleeping with Bridget Sullivan?

Despite what we see in Monster, there’s no historical evidence proving Lizzie Borden and Bridget Sullivan were in a sexual relationship. The theory has been around for decades, but it’s essentially speculation that has become part of the Lizzie Borden legend over time.

In reality, Bridget – who Lizzie and her sister Emma called “Maggie” – was a 26-year-old Irish immigrant who had worked as the Borden family’s live-in maid for nearly three years by the time of the murders. While her trial testimony gives us plenty of detail about life inside the house, nothing suggests she and Lizzie were lovers.

As for where the affair theory originated, one of the biggest sources came nearly 100 years later thanks to author Evan Hunter – better known by his pen name Ed McBain – who depicted Lizzie and Bridget as lovers in his fictional 1984 novel Lizzie.

The story sees Lizzie killing her parents after they find out about her relationship with Bridget. Although this was entirely made up, Hunter later explained that his theory was partly inspired by reports about Lizzie’s later friendship – and rumoured romance – with actress Nance O’Neil.

But that was his interpretation of events, rather than evidence that anything sexual happened between Lizzie and Bridget in the 1890s.

Author Sarah Miller – who wrote the 2016 nonfiction book The Borden Murders – is blunt when it comes to the claims. On the theory that Lizzie Borden was a lesbian and she murdered her parents because they discovered her secret, Miller said it’s “unsubstantiated”.

“This theory relies almost entirely on stereotype and innuendo,” Miller wrote, before listing where it’s derived from, starting with the fact that Lizzie never married. If there were any suitors, men or women, their names are lost to history.

In short, Lizzie and Bridget could technically have had a relationship nobody knew about. But there’s a pretty significant difference between something being possible and there being evidence it actually happened.

What do we actually know about Lizzie Borden’s sexuality?

Not a great deal. As said, Lizzie never got married, and there has been speculation for decades that she was attracted to women, but historians have no definitive evidence that allows us to confidently label her sexuality more than a century later.

A lot of that speculation centres not on Bridget, but on actress Nance O’Neil – played by Jessica Barden in the Netflix series.

Nance was a hugely successful stage actress, and Lizzie – who loved the theatre – became fascinated by her performances before the two women became friends in around 1904.

Their friendship was public enough to attract gossip at the time, and Lizzie entertained Nance and members of her theatre company at her home. It also coincided with Lizzie’s estrangement from her sister Emma, who moved out of their home in 1905 and never returned.

Miller wrote that this combination of incidents is what fuelled theories that Lizzie and Nance were more than just friends.

But again, there’s no proof of a sexual relationship. On June 10, 1927, shortly after Lizzie died, Nance spoke with the New Bedford Standard, with the report describing the women as friends.

Nance explained they had lost touch after she left the area, saying, “I am afraid I am a rather poor correspondent… We were like ships that pass in the night and speak each other in passing.”

Was Bridget Sullivan suspected of being involved in the murders?

While Bridget was questioned extensively and has been featured in later theories about the murders, she was never charged as her accomplice – in fact, she was an important prosecution witness.

Bridget was one of very few people known to be on the property that morning. She testified that she had been washing windows before Andrew returned home. She let him in and continued cleaning before going upstairs to rest.

Shortly after that, she said she heard Lizzie calling her downstairs because her father had been killed. Bridget’s testimony was important for the prosecution as she placed Lizzie at home at the time of the killings and claimed she hadn’t seen anyone else there.

That said, some of her testimony actually helped with Lizzie’s defence. The prosecution were attempting to establish Lizzie had a troubled relationship with her stepmother, but Bridget said they interacted “very civilly” and she never saw any “quarreling”.

She also provided one of the most intriguing details about the aftermath. After Andrew’s body was discovered, Bridget said, “I did not see any blood on her. Not on her face or hands, or anywhere. As far as I can remember, her hair was in order.”

Of course, none of this stopped speculation about Bridget in the years that followed. Some have suggested she helped Lizzie or covered up what she knew, while others have suggested that Bridget herself was the killer.

Author Len Rebello’s 1999 book Lizzie Borden: Past & Present records a theory by Mary D. Smith, originally published in The Armchair Detective in 1978, which proposed that Lizzie and Bridget were “partners in crime”. And Hunter’s later novel similarly turned Bridget into Lizzie’s lover and accomplice.

However, none of this proves that the real Bridget was involved in any way. And there could be a far less scandalous reason why she portrayed the life inside the Borden household as so harmonious when it clearly wasn’t.

When asked why Bridget would lie if she’s not involved in the crime, Killing the Bordens author C. Cree told Vanity Fair recently, “Because she was a live-in domestic servant and she wanted to continue to get work.”

But why does Monster make Lizzie and Bridget lovers?

Essentially, the creators of Monster: The Lizzie Borden Story felt the theory was simply too interesting to leave out of the Netflix series.

Speaking to Vanity Fair, Monster co-creator Ian Brennan said, “There’s some adage – absence of evidence is not evidence of absence.” The outlet specifically referenced Hunter’s 1984 novel, in which Lizzie and Bridget are lovers whose relationship is discovered by Abby.

“It just screams Boston marriage to me and it seemed too rich to ignore,” Brennan added. “I felt like we were ethically and morally excused to take that for granted. I think it’s one of the smaller leaps that we take in the show.”

But the relationship also serves a much bigger purpose within the show. Lizzie is someone who’s been intensely sheltered and repressed, and so meeting someone with Bridget’s more modern outlook is liberating for her.

As Brennan told TV Insider, “Bridget is really a catalyst. She’s like a foreign object that gets introduced to this ecosystem, and completely turns it on its head. I think Lizzie’s just completely perplexed [by Bridget] at first. She becomes, very quickly, an object of deep fascination and then desire.”