Image copyright Philadelphia City Archives Image caption Hannah Mary Tabbs and her supposed accomplice's mugshots from 1887

In 1887, the discovery of a torso near Philadelphia, Pennsylvania, touched off a sensational murder trial. Kali Nicole Gross, author of Hannah Mary Tabbs and the Disembodied Torso, went in search of the woman at the centre of it all.

When a local carpenter on his way to work discovered a headless, limbless, racially ambiguous torso in a pond just outside of Philadelphia, Pennsylvania, in 1887, it terrified the residents in the surrounding communities.

Though it seemed like the kind of crime likely to go unsolved, police quickly zeroed in on a black migrant named Hannah Mary Tabbs. Her trial lasted for months with an outcome few could have predicted.

Dubbed a "murderess", Tabbs and the torso case would be front-page news for months because it unearthed otherwise forbidden subjects such as adultery, sex and domestic violence. The victim was thought to be her lover, but Tabbs blamed an 18-year-old mixed-race teenager named George Wilson for the crime. Their fates became intertwined within the brutally racist criminal justice system of the time.

After first reading about the case in a century-and-half old Eastern State Penitentiary scrapbook, I was desperate to learn more about Tabbs, a married woman who at the very least had been involved in a deadly, adulterous love triangle with a man ten years her junior.

Image copyright Albert Vecerka Image caption An old scrapbook at Eastern State Penitentiary in Philadelphia offered clues

Tabbs was a kind of black woman that I hadn't encountered before while studying history. She knew how to put up a front when it came to respectability, but she also knew how to manipulate, threaten, and brutalise people to get what she wanted - whether it was to be feared or to engage in a risqué affair.

After I decided to write about her, there were many moments when other scholars belittled the project. Some ridiculed the notion of documenting the story outright while many publishers passed on the project because Tabbs was "not sympathetic". I especially chafed at this. Was Lizzie Borden expected to be sympathetic? Why ask this of Tabbs? Did black women have to be purely good or purely victims for a mainstream audience to care about their history?

But perhaps more importantly, why did they see her as undeserving of sympathy?

Hannah Mary Tabbs was born in the 1850s in a slave state and grew into her womanhood during the nation's bloody Civil War. When she met her husband, a man 15 years older, she was alone in Baltimore, Maryland, with her "mulatto niece" in tow. Some questioned whether Tabbs was the girl's mother. If so, I wondered about the circumstances of conception - had she been raped or otherwise exploited?

Image copyright New York Freeman Image caption A story in the New York Freeman dated March 1887

Her exploits in Philadelphia, particularly how she bullied, and viciously and routinely beat those in her family and neighbourhood, all gesture toward eyes that have seen too much. Her ability to wield violence in these ways suggested past victimization as much as it testified to her brutality.

I tried to uncover as much as I could about her early history, but Tabbs didn't make this easy. She used aliases, gave false information about her nativity, changed her age, and generally relied on lies and misdirection to reach her goals.

Her prison records and a number of press accounts listed her birthplace as Virginia. She told authorities she was from Richmond, but there was no trace of her at the Virginia Historical Society and other area archives.

I read every press account imaginable, in papers from Philadelphia to Ohio to Missouri to New York. Surprisingly, it was a German language paper that revealed she was in fact from Ann Arundel County, Maryland. It was at the Maryland State Archives in Annapolis that I finally found her marriage records and her maiden name - Hannah Ann Smith.

Her Civil War Widow's Pension file from the National Archives in Washington, DC, would be my greatest find - it contained detailed affidavits from Tabbs and those who knew about her married years, it had a copy of her marriage certificate from 1874, and it had her signature.

For me, her story, her bad acts, and her flaws showcase her humanity and her profound vulnerability. In era when black women's bodies were never their own, there were all kinds of reasons being feared was a good thing. But her case also opened a window into the impact of biased justice and its role in urban crime that are still very much at play today.

Image copyright The National Police Gazette Image caption The coroner brought in women of colour in an attempt to discern the victim's race

Despite the numerous assaults she committed in the black community, she had no criminal record - it wasn't until authorities believed that her victim was a white man that she found herself in the crosshairs of the justice system. The dynamics spotlight the chasm between the black community and adequate police protection.

Both Tabbs and the young man she implicated in the murder endured coercion and a lengthy interrogation in police custody - this shows the long history of black suspects being beaten into false confessions.

It's a story that proves how systemic racism was woven in the fabric of policing and the adjudication of crime throughout the history of this country. Facing this history means asking different questions about how best to stop profiling and brutality today.

Without question, Hannah Mary Tabbs is a disturbing figure. She did unconscionable things to grant herself pleasure and autonomy at a time when the prevailing message was that black women deserved anything but.

She muddies rigid notions of good and evil, and crime and justice.

I wrote a book about her for all of those reasons and this: I don't want black women to have to be clean in order to merit scholarly attention or to be legible as human beings. Studying figures that aren't customarily "good" serves as an affirmation of their - and ultimately our - humanity.

Kali Nicole Gross is the author of Hannah Mary Tabbs and the Disembodied Torso. She is a professor of African and African Diaspora Studies at the University of Texas.