Katherine Knight had a long history of violence towards the men in her life, all ramping up to the shockingly brutal murder of her boyfriend.

The night the Australian butcher married her first husband, David Kellett, she allegedly tried to strangle him. Then, while pregnant with her daughter, she torched his clothing and walloped him on the head with a frying pan. He eventually left her and she took up another man, David Saunders. She murdered his puppy in front of him as a warning, but he didn’t leave her until she stabbed him in the stomach with a pair of scissors during an argument.

In October of 2001, Knight, brutally stabbed her new live-in boyfriend, John Price, 37 times while he tried to escape. She then skinned him, hanging his skin from a meat hook, chopped him up, and started to cook his body parts. She set the table for a macabre dinner party with his children’s names on place cards. Price had been concerned that something like this would happen and had told his friends that if he didn’t show up at work the next day, Knight had killed him. When he wasn’t on the job, they called the police. When investigators searched her home, they found his head in a pot, boiling away on the stove with some vegetables. Knight was promptly arrested. She is now known as “Australia’s most notorious psychopath,” and became the first woman in Australian history to be sentenced to life without parole. A movie based on her life and crimes is currently in the works. 

All five of Betty Neumar’s husbands died, most of them mysteriously. When her first husband was shot in the head in 1970, almost two decades after their divorce, it was ruled a homicide but she wasn't charged. In the mid-1950s, her second husband had either “froze to death in a truck” or was shot to death “on a pier” in New York was a bit of a mystery. In 1965, her third husband shot himself in an apparent suicide, although that finding has been questioned as he may have been shot twice. Her fourth husband, Harold Gentry, was gunned down in their home in 1986. And when her fifth husband passed away in 2007, the state of Georgia investigated to determine if he was poisoned, but could find no evidence of Neumar’s involvement. His family did not agree with the finding. Neumar’s son also committed suicide in 1985, and Neumar was named as the beneficiary on his $10,000 life insurance policy.

It was the death of the fourth husband would eventually bring police to Neumar’s door. Gentry’s brother was convinced that Neumar was behind it, and urged police to re-open the case. They finally did in 2007, and Neumar was charged with hiring hitmen to kill her husband. As the police investigated her, they uncovered more and more mysteries. The former beautician and bus driver had multiple driver’s licenses, secret bank accounts, and passports and credit cards in other people’s names.

Before she could be tried – or answer any questions about her past or the fate of her many husbands – Neumar died of complications from cancer in 2011. She was 79.

Antifreeze was the preferred weapon for Stacey Castor. She had met her first husband, Michael Wallace, when she was just 17, and they married a few years later and had two daughters. Then, as their marriage crumbled, Wallace started to feel ill, dying in 2000 after a mysterious ailment. His doctors called it a heart attack, but the family was suspicious, at least in hindsight. In 2003, Castor married David Castor. Two years later, Castor called the police saying her suicidal husband had locked himself in the bedroom after an argument and she was concerned. They broke down the door and found David Castor dead with a bottle of antifreeze at his side. Castor buried him next to the body of her first husband in the same upstate New York cemetery. At first they thought suicide, but evidence soon started to mount that Castor had force-fed her husband the poison with a turkey baster. They exhumed Wallace’s body and found evidence of antifreeze poisoning as well.

As the police closed in, Castor panicked and decided to frame her daughter, Ashley Wallace, for the murder. She invited the 20 year old over for a drink, and dosed her with so many pills that she wound up in a coma for 17 hours. While her daughter was unconscious, Castor forged Wallace’s name on a suicide note in which she confessed to killing her father and David Castor. Police didn’t buy it, though, and Castor was arrested for murdering David and attempting to murder Ashley. She was convicted and sentenced to 51 years, but died in prison earlier this year. 

To this day, Chisako Kakehi, Japan’s most notorious black widow, insists she’s innocent. She claims that she’s not a serial killer but has been "doomed by fate" – though it's also possible that she is a ruthless murderer who systematically killed at least eight men for insurance money. According to Japanese authorities, between 1994 and 2013, at least seven men that Kakehi – a.k.a. "the Black Widow of Kyoto" – either dated or married died, leaving her alone, save for around $7 million in insurance payouts. Some of the deaths in her wake were originally deemed of natural causes (two husbands died of "unknown causes", one had a stroke, and a boyfriend died possibly of cancer), but when traces of cyanide were found in her new groom's dead body, police started to become very suspicious of the repeat widow. "Given their advanced age, we have to proceed carefully to judge whether their deaths were actually the result of foul play or not," an investigator told the AFP new service. So far, Kakehi has been charged with the 2013 murder of her husband, Isao Kakehi, 75, who collapsed in his home with cyanide in his system a month after their marriage, as well as in the death of her common law husband, 71-year-old Masanori Honda, who died in a motorcycle crash after she allegedly poisoned him. Last year, she was also charged in the attempted of a 78-year-old boyfriend, after she allegedly slipped hydrocyanic acid into his drink while they dined at a restaurant in 2007. He collapsed in a parking lot, but didn’t die until two years later. While police found a small bag of cyanide compounds in a plant pot she ditched at a recycling center near her home, Kakehi claims she has no idea how to kill someone. It’s safe to say that the police don’t believe her.