The Sneaky Serial Killer

Money, Murder and the Psychology of a Serial Poisoner

Joni E. Johnston, Psy. D.
7 min readMay 1, 2023
copyright free,courtesy of the Royal Thai Police

One person thought she was taking medication for Covid-19. Another thought she was consuming an herbal remedy. Yet another thought it was a diet aid. But Sararat “Am” Rangsiwuthaporn knew the truth. It was cyanide. They were all dead within minutes. And Sararat Rangsiwuthaporn had achieved her goal.

We often don’t think of women as serial killers. And perhaps that’s why, on average, they tend to kill more victims and get away with it longer than their male compadres. Accused female serial killer Sararat “Am” Rangsiwuthaporn from Thailand is a good example; if she is found guilty of everything she’s accused of, she has murdered eleven people in the past two and a half years. She almost killed two more.

A Protection Ritual Fails

Here’s how she was caught. On Tuesday, April 27, 2023, the Royal Thai Police arrested the thirty-six-year-old Rangsiwuthaporn for the murder of her friend, Siriporn Khanwong. The two had been on a trip together. Shortly after the two of them had participated in a Buddhist protection ritual of releasing fish into the Mae Kong River, Siriporn collapsed on the riverbank and died. Her phone, money, and belongings disappeared.

To Siriporn’s relatives, her death made no sense. She had been the picture of health, having given birth to her second child just a few weeks earlier. They shared their suspicions with the police, who started an investigation and ordered an autopsy.

An autopsy discovered that Siriporn died of cyanide poisoning. A downside of using cyanide, from a murderer’s perspective, is that a lethal amount hangs around in the body for months after ingestion. Traces of it were also found in the Honda Civic Ms. Sararat and her ex-husband used to drive, as well as a Toyota she was driving during her trip with Siriporn Khanwong. A search of her home also turned up a substance investigators believe is cyanide, leading investigators to believe she poisoned the food and drink of some of her victims.

The Royal Thai Police felt like they had their killer and charged Sararat with her friend’s murder. As their investigation continued, they were stunned to uncover a money trail that led to several dead people’s bank accounts. Apparently, lending Sararat money was a deadly good deed; when the bill was due, the lender often dropped dead. They also found that Sararat had been involved in a number of shady financial dealings, had stolen jewelry and valuables from some of her victims, and suspected that she lured them into her schemes and then poisoned them.

Police are still investigating the numbers and circumstances, but — so far — up to twenty people have been identified as potential victims. Among these are a former partner, two female police officers, and a policeman’s wife. Cyanide has been found in recent autopsies.

She has already been charged with three counts of premeditated murder, orchestrating a murder, and theft. As of 04/30.2023, Thai police are seeking eight more arrest warrants for premeditated murder. While the scope of her alleged victim pool is undetermined, they include lovers, friends, and acquaintances. But the common motive was money.

The Psychology of a Poisoner

So who is this woman who allegedly killed over a dozen people in such a short span?

I must admit that poison as a murder weapon has always intrigued me. Perhaps it’s history; for hundreds of years, poison has been a convenient way to hurry up an inheritance or eliminate an unwanted spouse. Maybe it’s the secrecy; despite this, we’ve known very little about the personality of the criminal poisoner.

Part of the problem may be the skill with which many poisoners have eluded authority (it wasn’t until the twentieth century that we were any good at catching them). It may partly be due to misguided stereotypes about who uses poison to kill. (Do women really use poison more often than men?). And it may partly be that because poisoning someone usually requires a sophisticated plan (as opposed to picking up a baseball bat or grabbing a gun), we’ve confused the intelligence of the perpetrator with their personality.

But we’re starting to learn about the ones who’ve been caught. Experts believe the number of poisoners who elude justice is twenty to thirty times higher than those behind bars. Still, we can make some educated guesses about the personalities of poisoners by studying the nature of convicted poisoners and the crimes they commit. Better the devil you know.

The Demographics of Death

It should come as no surprise that women often get blamed for things men do, even in the face of overwhelming evidence to the contrary. In 1984, French author Alexandre Dumas ( The Three Musketeers) wrote a detective fiction novel in which the protagonist repeatedly tells his stumped colleagues, “Cherchez la femme.” Look for the woman.” Even though, for time eternal, murder has been a male-dominated activity.

So here’s what we know so far. When the murder victim is a woman, most poisoners are men. When the victim is a man, the split is about fifty-fifty. Poisoners tend to stab people of the same race; white poisoners tend to poison white victims; African Americans tend to poison each other, and so on. (This is also true of shooters, stabbers, and stranglers). On average, a poisoner manages to kill someone slightly older (five to ten years) than they are.

Plenty of poisoners got their pre-murder practice in the medical field; there are more poisonous doctors, nurses, chemists, and lab techs than you might expect. There are also plenty in caretaking roles; parent, spouse, nursing home attendant, where there’s the deadly duo of easy access to fatal substances and vulnerable victims. This assumption has been especially true in recent times when choosing exotic poisons like arsenic and cyanide has given way to the use of everyday household products like Visine and antifreeze.

The Poisonous Personality

“It’s always the quiet ones.” This excerpt from is from serial poisoner Rachel Staudte’s diary. In 2012, she and her mother, Diane, murdered Dad Mark and brother Shaun by spiking their drinks with antifreeze. They were on the way to wiping out the entire family (including a twelve-year-old sister) when they took daughter and sister Sara to the emergency room after dosing her with the same drug — not to save her life but because Rachel was “grossed out” by the thought of her sister dying in the house.

Rachel’s inner musings not only reveal something about her. They tell us something about poisoners in general. As a group, murderers who choose poison as a weapon are not drama queens. They don’t throw temper tantrums. No one thinks of them as a powder keg or a bully. Because they tend to avoid confrontation, other people see them as easygoing and somewhat passive.

But that’s because poisoners tend to operate behind the scenes. Behind that pleasant façade lurks an immature personality determined to get their way and using emotional and verbal manipulation to do so. Guilt, gaslighting, and playing the victim are the weapons poisoners tend to use before they become deadly.

Poisoners also tend to be clever. I’ve seen poisoners design a murder plan in as much detail as a scriptwriter would lay out a script. Perhaps it’s all the hours they spend daydreaming about how much better life would be if a spouse disappeared or the inheritance came early or a troublesome boss dropped dead that primes the pump for an eventual murder plot. By its very nature, killing someone with poison requires planning and deception, so it’s no surprise that poisoners tend to be cunning, sneaky, and creative.

When we look at the childhood of convicted poisoners, we tend to find extremes, either an upbringing rife with trauma or one filled with overindulgence and lacking consequences. Underneath their pleasant demeanor, many poisoners feel entitled to get whatever they want. Their narcissism leaves little room for genuine empathy, and their actions, often disguised as altruism or self-sacrifice, are, in reality, guided by self-interest.

The vast majority of poisoners kill someone they know; a child, spouse, friend, or acquaintance. Their motives are much different from other murderers; they usually revolve around money (life insurance, avoiding alimony or property splitting); jealousy (“lover’s triangle”); convenience (she’ll marry me if I get rid of the kids) revenge (he’ll pay for dumping me); political conviction ( assassination, terrorism) boredom (let’s see if I can get away with it); and ego (belief in mental superiority).

Some serial poisoners have some pretty twisted psychological kinks. Some healthcare serial poisoners have gotten off on playing the role of tender, self-sacrificing attendant to the person they’re slowly killing. Think of Jane Toppan and Dr. Harold Shipman, whose dutiful ministrations to their victims initially aroused tears and gratitude from family members.

There is a form of medical child abuse formerly know n as Munchausen by Proxy, in which a perpetrator harms a child to attract sympathy and attention from others. In some cases, poison has been used. And then there’s outlier Graham Frederick Young, whose interest in chemistry turned into a deadly obsession as he conducted real-life experiments (keeping detailed notes) on unsuspecting friends and family members.

The Bottom Line

Given that 1 out of 5 poison murders is never solved, it’s hard to profile the “typical” poisoner. Those who’ve been caught and convicted give us some clues — clever, sneaky, emotionally immature, organized, and self-centered. Many of them are amazingly skilled at pretending to be something they’re not — a doting husband, caring nurse, or devoted friend. While poisoners’ motives vary, greed is, for many, an insatiable hunger. A poisoner who has nibbled on fraud, embezzlement, or pyramid schemes in the past may feast on murder when it’s so tempting to slip a deadly subtance into an unsuspecting victim’s food or drink.



Joni E. Johnston, Psy. D.

Forensic psychologist/private investigator//author of serial killer book. Passionate about victim’s rights, the psychology of true crime, and criminal justice.