Inside Thailand’s cyanide murders and the search for its ‘most prolific serial killer’ in history

Inside Thailand’s cyanide murders and the search for its ‘most prolific serial killer’ in history When healthy people suddenly began dying, grieving families struggled to get answers. The series, Death Loans, retraces how a dogged investigator looking into a friend’s death helped police connect 15 cases to one woman eventually. BANGKOK: When her friend gave her some herbal medicine for her cough, Kantima “Pla” Paesaard did not think too much about it. She wasn’t to know it would turn out to be an alleged murder attempt. Less than 10 minutes after they went their separate ways, Pla started feeling short of breath. So she turned on the air-conditioner in her car and got a strong draught blowing at her face. “But no matter how I tried to breathe, I still couldn’t,” she recalled. After she called an ambulance, her hands started to stiffen. When the ambulance arrived a few minutes later, only her little finger could move a bit, she said. And once she was in the ambulance, “everything just went black”. Hours went by before she started to awake. “After I regained consciousness, my husband told me, ‘Do you know that earlier, your heart had actually stopped beating?’” she recounted. “The doctor told me they did a brain scan. They checked my blood and examined my whole body, and there was nothing abnormal. So I thought it was an allergic reaction to the herbal medicine.” Her friend, Sararat “Aem” Rangsiwuthaporn, checked on her in hospital, seemingly worried for her health. Pla did not suspect anything. They had known each other for about 10 years. Their husbands — or ex-husband, in Aem’s case — were from the same police academy class. “I felt like Aem was part of the family. We’d always visit each other,” she said. Two months later, in November 2022, when the two friends went to a gathering together, Pla’s mum asked Aem (also spelt as Am) why she looked thinner. Weight-loss pills, she replied. “So my mum said, ‘If that’s the case, bring some for Pla to try so she can lose weight too,’” Pla recounted. After the gathering ended, Aem brought over the pills to their house in Thailand’s Kanchanaburi province. But Pla chose not to take them. She still did not have any suspicions of her friend, not until she heard the news about a woman who had been poisoned with cyanide months later, with Aem present at the scene. Pla, then 36, started googling the symptoms of cyanide poisoning and found that they included difficulty breathing and stiff hands. “At that moment, I was very shocked,” she said. She was the only survivor out of 15 victims identified by the police in what has become a historic set of cases, involving a pattern of deaths in different provinces starting as far back as 2015. Aem, now 39, is the “most prolific serial killer in Thai history”, according to Surachate Hakparn, the deputy police chief from 2022 to 2024. “She’s killed more people than Jack the Ripper, the Zodiac and BTK (did individually),” he charged. Only one of those three — BTK (Bind, Torture, Kill), the moniker for American killer Dennis Rader — was caught. And it took one of the largest investigations ever conducted in Thailand for the Royal Thai Police to catch their killer better known as Aem Cyanide. The series, Death Loans, tells how the country’s cyanide murders finally ended. WATCH PART 1: ‘She didn’t go alone’ — This CCTV footage helped expose Thai serial killer (46:57) MYSTERIOUS DEATHS Most of the victims were in their 30s and healthy. All died under mysterious circumstances. In Mukdahan province, Sawitree “Nim” Budsrirak, 40, had just given birth to a baby girl, “exactly as we’d hoped”, said her husband, Nitipon “Ta” Nuchit. A month later, in November 2020, he was back at work in Bangkok, 650km away. Nim was taking care of the children — their newborn and their five-year-old son — and cleaning the house. One day when he was on his break, he tried video-calling Nim. She did not answer. Then he sent her a message. It was left unread. So he video-called his son, Neo. “I asked him, ‘Who are you with? Where’s Mummy? I want to talk to Mummy.’ Neo turned the camera towards the mattress. I saw Nim lying face down, with her face resting on the edge of the mattress,” he recounted. I called out to Nim several times, but she didn’t get up. Thinking that Nim was tired and had taken a nap, he decided to end the call. “After no more than 30 minutes, I tried video-calling again,” he continued. “Neo answered as before and turned the camera towards Nim, who was still lying in the same position. That’s when I realised something was wrong.” He immediately called a neighbour to check on Nim. Her lips had turned dark bluish, a trickle of blood was oozing from her mouth, and her body was covered in sweat. “Nim was found dead on the bed while our daughter was sleeping only a few feet away,” Ta said. “Nim was playing just fine with the children. It’s impossible that she’d then die. How could something like this happen?” At that time, he wasn’t to know the answer lay in Thailand’s money-sharing circles. These are rotating savings groups whose members save together. The money they contribute regularly is pooled, which members can borrow when needed. These loans are not free. Members pay a monthly interest — setting the rate themselves beforehand — on loans taken out from the group’s fund. They must also continue their regular contributions as they repay the loans. “It’s estimated that millions of Thais participate in share groups, with billions of baht estimated to be in circulation,” said Piriya Pholphirul, an economics professor at the National Institute of Development Administration. Nim was one of them, joining in as a way of earning additional income, said Ta. Sharing circles have existed for generations, built on friendship and trust. But the problem was that she joined an online sharing group with Aem. For another victim, Surat “Bee” Toraphap, 35, his friendship with Aem went back to childhood. They had been schoolmates. In January 2021, his brother “Koon” was at a temple when a neighbour in Kanchanaburi’s Tha Maka district called to say that Bee was in the bathroom and turning blue. Koon hurried over. “There were police all over the house. I saw my younger sibling sitting on the toilet in the bathroom, leaning to the right. I realised my sibling was no longer with me,” he said. “My younger brother was healthy, didn’t drink and didn’t smoke. His death was abnormal. I started getting suspicious and unlocked my brother’s phone and wondered why this friend named ‘Aem’ wasn’t responding to him.” It turned out that Bee had lent her money: 50,000 baht (US$1,500) at first and then another 10,000 baht. But for all of Koon’s suspicions, his brother’s death was classified as natural, as was the case for Nim and other victims. THE CASE THAT BLEW IT ALL WIDE OPEN Aem’s victims could be categorised in a few groups, such as those in savings groups where she was the organiser, those whom she borrowed money from and those who loaned her money to lend out to others. One of the people she invited to lend money through her was her friend Siriporn “Koy” Khanwong, 32. On Apr 14, 2023, Koy told her mother she was going to run an errand. “She told me to wait,” recalled Thongpin Kiatchanasiri. “She said she’d come back in the evening and take me shopping. But she never came back.” Koy had two phones. “If one phone was off, the other one would still be on,” said her elder sister, Nipawan “Som” Khanwong. “But that day, both phones were off at the same time. I was so anxious, wondering why.” As Koy’s family tried to figure out where she was, a friend of hers, independent investigator Rapee Chamnanrua, received a photo of a person the police in Ratchaburi province were trying to identify. It was Koy. She had fainted and died by the Mae Klong River, 80km west of Bangkok. The police cited the official cause of death as a heart attack. But her mother “didn’t believe that her heart would fail”. “My daughter was only 32, healthy and strong,” said Thongpin, now 65. “I was shocked. I felt I was losing my sanity. … I kept asking where her bag went, where her phone went, because they were all gone.” Som also “felt something was wrong”, but the police “wouldn’t listen”, she recounted. The family’s request for a further probe into Koy’s death was turned down. Her body was returned to them the next day for Buddhist rites and cremation. The first person who listened to the family and thought her death was unnatural was Rapee. “How could someone so young just die so suddenly?” he questioned. “Because I knew her, this case was special (to me).” But at first, his investigation went down the wrong path. The family suspected a former boyfriend who had allegedly threatened her. This was a police officer named Navin — whose alibi ruled him out, according to the police. Doubting that the police would implicate one of their own, Rapee “asked people to go check on Navin”. He reasoned: “Navin had an intimate relationship with Koy.” Above all else, however, he wanted “someone in authority” to hear the family out before her cremation. So they met the police general Surachate, who is known in Thailand by his nickname, “Big Joke”. “I put all the evidence in front of him and asked him if he felt the local police had done their job,” recounted Rapee, who cited Koy’s missing belongings, among other things. “A heart attack doesn’t make belongings disappear.” Surachate gave credit to Rapee for getting him involved in the case. His own suspicions were aroused when Rapee showed him the autopsy report, which recorded that Koy was healthy. “This was unusual,” he said, adding that Navin’s alleged threats were also “concerning”. Things started moving “much faster” after Surachate got involved in the case, said Som. For example, the police called her in to watch the footage from the closed-circuit television cameras pointed towards the walkway along the river. Rapee said they were “very lucky” because the cameras had been recently repaired after being “broken for a long time”. Meanwhile, a second, more detailed autopsy was performed on Koy. When the toxicology results came out, forensic pathologist Smith Srisont, who ran the test, “was very shocked”. It was a cyanide poisoning case. His colleague at Ramathibodi Hospital, internal medicine doctor Sahaphume Srisuma, had “never seen this before” in his practice in Thailand. “Cyanide is one of the most lethal chemical compounds known to mankind. It’s virtually untraceable,” said Sahaphume. “The most dangerous thing is cyanide is lethal either by ingestion or inhalation. All it takes is a tiny dose, maybe smaller than a grain of rice.” That was not the only evidence that “changed the case immediately” as Surachate described. CCTV footage showed that when Koy went to release fish at the Mae Klong pier, she did not go alone. She was with Aem. UNMASKING A SERIAL KILLER It turned out Koy had transferred 300,000 baht to Aem for her to invest “because she was a friend and we trusted her”, said Som, who shared that she herself first met Aem at age 16. “Aem was very chatty, and she got along with people easily,” Som added. “But her personality changed when it came to money. She started getting involved with money matters, talking about it, pushing it, things like that.” Aem’s financial motives led the police to follow the money trail, which eventually led to gambling websites and gambling dens. “I’ll give one example. She was travelling from Kanchanaburi to Nakhon Pathom. She found a gambling den along the way. She goes straight in, plays and loses 10 million baht,” cited Surachate. “Whose money was that? Money she’d just borrowed from people.” Online savings groups and instant bank transfers — plus misplaced trust — allowed money to move with ease and feed her gambling addiction. “When asked to repay, if there’s no money to clear debts, what do you do?” remarked Surachate. Citing what he learnt from the Federal Bureau of Investigation, he added: “Serial killers, if they’re men, will commit crimes outside the city, and the motive is sexual in nature. But if it’s a woman, the motive must be money.” Prior to Aem, there was the case of serial killer Somkid Phumphuang, who raped and killed his victims — six of them — between 2005 and 2019. There are “many contributing factors”, however, in cases like Aem, according to Somdet Chaopraya Institute of Psychiatry deputy director Winyoo Chanakul, who has over 20 years’ experience in caring for psychiatric patients who have committed violent acts or even homicide. “Someone who has financial problems to the point of being able to kill others, and to do so repeatedly, can’t be explained by financial reasons alone. Otherwise, everyone in debt would be killing people,” he said. “The person must have certain personality traits that allow them to commit serious wrongdoing for their own benefit without feeling guilt. This includes a lack of empathy and a disregard for social rules.” Thinking back on Aem’s personality, Som remembered her once saying that if anyone were to fight with her or say something bad, “she wouldn’t let it go” and would “go as far as killing”. When the police arrested Aem, however, senior staff writer Pravit Rojanaphruk at news outlet Khaosod English remembers that “everyone was confused” by this woman from a middle-class background. “She looks just like anyone from an average neighbourhood,” he said. “How could this woman be a killer?” It became a major news story that many people have followed. “No one person has caused this much of an uproar before,” he added, citing the 14 murder charges. She has contested all the charges so far. One of her lawyers, Thannicha “Pat” Aeksuwannawat, said it was “impossible that Aem committed all 14 murders”. “The police want to dump the murder cases onto Aem so they don’t have to find the real perpetrator. It was clear that she was being targeted,” said Pat. “It’s media-driven momentum more than facts. “They said death was due to cyanide. … That cyanide mightn’t have come from Aem. This is the weakness of the case.” Buying cyanide in Thailand is not suspicious on its own. It is used in factories in metal-related industries, such as for metal plating and electroplating. It is used in gold shops and in research. And what the police found was that Aem “never used her own name to order cyanide”, said Surachate. “She had others order it, and then it reached her.” But how did it reach her? One of the cyanide bottles that the police seized had been sold by a company that called Grab to do the delivery. And the rider took a photo when delivering the cyanide to Aem in her Toyota Fortuner, recounted Rapee. “In that photo, a small pink Hello Kitty bag was visible beside the gear stick. Once the police … impounded the bag, we found this bottle,” he said, adding that the bottle had a registration number showing who the importer was. “Aem used her phone number to contact the company. All the evidence pointed directly to Aem. Game over.” TRIALS, TRIBUTES, TRIBULATIONS Although Rapee said it was Aem’s “own mistakes that brought her down”, his involvement led to a breakthrough in the case in more ways than one. After he and Koy’s family appealed publicly for information once Aem was fingered as a suspect, his phone began ringing nonstop. Families across Thailand told of similar stories: sudden deaths, missing money and a connection to savings groups. One of those who came forward was Pla. She said Aem had asked for a loan to repay a fund, so she gave her 250,000 baht. “She was my friend. Why would I refuse?” said Pla. But she was lending the money only for a month. Then she asked Aem to return the entire amount as agreed because she had to pay for her car. “Reliving my ordeal wasn’t easy,” said Pla, who did it so that Aem “won’t be able to hurt anyone else again”. Pravit described her role as the “nail in the coffin” for Aem, who was sentenced to death in November 2024 for the murder of Koy. WATCH PART 2: ‘She tried to kill me twice’ — The witness who survived a serial killer (46:59) It is a penalty she deserves, said Thongpin, who was “very close” to Koy. “We’d travel together, perform Buddhist rituals together.” Koy and her sister were also close. Som called her the “pillar of the family” who took care of everyone. “Koy only had one child, so she doted on her. She loved her so much. Whatever the child wanted, she got,” said Som, referring to Koy’s daughter, now 13. “Everything she built, she built it for her daughter.” The murders of Nim and Bee, meanwhile, have not gone to trial yet. Koon said he thinks about his younger brother every day. “And whenever I do, my heart feels as if it’s going to break,” he lamented. As for Ta, if he had the chance, he would want to speak to Nim — whom he lovingly described as “good-hearted” and “always willing to help others” — one more time. “I’d want to thank her for coming into my life as my wife and as the mother of our children, for making my life better and helping me grow and become more mature,” he said. As of Sep 22, the criminal court has delivered three death sentences and two life imprisonments for Aem’s string of cyanide murders, plus acquittals in three cases where the court cited a lack of evidence in her favour. Since the end of 2009, Thailand has carried out only one execution, in 2018, even as several death sentences have been imposed. Aem’s next trial date is Nov 25, for the attempted murder of Pla. Watch Part 1 and Part 2 of the series, Death Loans: Thailand’s Cyanide Murders.