Katarzyna Onyszkiewiczowa was born around 1840 from a humble peasant family in Chernivtsi (then part of Austrian Galicia, now in Ukraine), born to parents possibly named Jan and Marynia Onyszkiewicz, and raised Greek Catholic. She likely earned her initial living as a seamstress, a modest but respectable trade.

Her first recorded brush with the law came in 1858, when she was convicted of theft in Chernivtsi and handed a six-month prison sentence. The very next year, in Śniatyn, she was again convicted for theft, but this time the punishment also included 20 lashes with a rod, highlighting both the severity of her crime and the harsh nature of justice in rural Galicia back then.

These early infractions mark the emergence of a pattern: petty theft, but with escalating daring. Upon her release, Katarzyna seemed to morph into an itinerant figure, a traveling con‑artist of sorts, who crisscrossed villages, posing as either a humble merchant or even a nun, tapping into hosts’ sympathy to secure shelter. 

By the late 1850s, Onyszkiewiczowa had already logged two convictions for theft: a six-month sentence in Chernivtsi (1858), followed by another in Śniatyn in 1859, where she received 20 lashes with a rod. These early infractions, while minor, reveal a criminal streak and the kind of punishment typical in rural Galicia.

After release, she quietly pivoted to a more cunning and lethal crime pattern. Traveling from village to village, posing alternately as a merchant or a nun, she was frequently welcomed into people’s homes under the guise of piety or commerce. Her hospitality was a trap: she served male homeowners a deadly brew, allegedly made of jimsonweed, cowbane, and henbane, which induced paralysis, hallucinations, convulsions, vomiting, and respiratory failure. Many victims collapsed unconscious; some never regained life. Once the victims were incapacitated or dead, she would ransack their homes for valuables and vanish into the night.

Her criminal spree ultimately caught up with her. In 1869, she was convicted of murder in Stanisławów (Ivano-Frankivsk) and sentenced to ten years in Lviv’s Mary Magdalene Prison, housed within a convent-like facility for women. Undeterred, she executed a daring prison escape on July 9, 1870, breaking free alongside Barbara Woźna, another female inmate.

On the run, she struck again as reports say she committed poisoning-theft crimes in several villages, resulting in at least two more deaths.

Authorities mounted a swift manhunt. Commissioner Meidinger and agent Millet chased her through countryside and rail lines all the way to Kraków, where she was finally arrested on 7 November 1870. Much of the stolen haul, hundreds of zlotys in gold, silver, and banknotes, was recovered from her person.

Back in Lviv, she received a second ten-year sentence, to be served after her current term. Nine years into her incarceration, she staged yet another dramatic escape on the night of  September 2–3, 1879, she vanished again from Lviv prison.

On September 18, 1879, a local postmaster recognized her at a fair in Podkamien (Pidhaytsi region). Despite her denial, his suspicion stirred an alert and she was captured days later in Monastyryska.

Her February 1880 trial, back in Lviv, became a media spectacle. Newspapers swarmed the courthouse, reporting that every inch of seating and gallery space was claimed well ahead of time; over 160 tickets were issued just for seats among standing spectators.

At the stand, she staked out her identity, claiming she was once called Rózia, from Bukovina, daughter of Marynia; made a living by sewing; illiterate, once serving a local noble.

Public prosecutor Mr. Henzel and defense attorney Dr. Krówczyński squared off in a courtroom packed with intrigue. During testimony, prosecutors laid out her long pattern of poisoning-related thefts, not just the final murders, but a lengthy criminal arc involving 20 poisoning thefts right after her 1866 release.

Her story finally ended quietly in Lviv prison. On March 9, 1895, she died behind bars.