Episode 167:
14 Friends and Lovers Dead After Eating What She Gave Them, Female Serial Killer in Thailand
On the morning of April 14, 2023, Songkran, the Thai New Year, a 32-year-old woman named Siriporn left her home in Kanchanaburi province, Thailand. Everyone called her Koy. She told her mother she was going to the river with a friend called Am to release fish, a Buddhist act of merit, and would be back to take her shopping that evening. Koy ran her own small business and was always on her phone. That day she stopped answering.
Her older sister called Am, who said they had no plans that day and that she was in Ayutthaya, 125 miles away. At 2 p.m. the sister posted on Facebook asking for help finding Koy. Someone replied with another post: a hospital was looking for the family of an unidentified woman. It was Koy. Police told the family she had most likely had a heart attack.
The Footage at the Pier
Koy's chin had a bluish-green mark, her lips were discolored, and her fingernails had turned black. Her car, her Louis Vuitton bag, her phone and cash worth about $5,000 were gone. When the family asked for the pier's security footage, police said there were no cameras. Koy's brother went to the pier and found several. The footage showed a car pulling up by the river with a woman at the wheel. Koy got out of the passenger side holding a bag of fish and walked down the stairs to the pier. The driver crossed to the other side of the street, kept looking around, asked a passerby where the restroom was, and did not go. She went back to the car, took something out, and walked down to the same pier. Ten seconds later she came back up holding Koy's phone, told people nearby that someone had collapsed, and drove away. Police said she had not been with Koy at the moment of death, that the death had already been ruled a heart attack, and that the car's registration had been cancelled so the owner could not be traced. The family filed a complaint with criminal investigators and requested a full autopsy with toxicology, which they were told would take thirty days. The police investigated only the missing belongings.
The Facebook Post
Rapee, a volunteer with a civic group known for helping people the system had failed, took up the case. Koy had driven her own car that morning, so she must have switched cars somewhere. Tracing roadside cameras, he and the family found where: in front of a house, and on the way to the river the two women had stopped at a gas station to buy drinks. The footage was too poor to identify the driver, so Rapee posted everything on Facebook, including her image outside the house. Tips arrived at once. The house belonged to a deputy police chief named Withoon, and the woman was his ex-wife, 36-year-old Sararat Rangsiwuthaporn. Her nickname was Am. She was the friend Koy had said she was meeting. On the day Koy died, Am had called Koy's sister to offer sympathy and asked whether police had any suspects and what the autopsy showed. When Rapee called her, she repeated that she had been in Ayutthaya. Two days later she called him back, said she had seen his post, and admitted she had been with Koy. Koy had clutched her chest and collapsed, she said, and she had lied because she feared the family would blame her. Asked about the Louis Vuitton bag, she said she had left it outside Koy's house, then that she had thrown it in the trash. Police charged her only with theft, and she was released on bail. Then Koy's blood results came back, in ten days rather than thirty. She had died of cyanide poisoning. With public outrage building, police arrested Am for premeditated murder. Am was living in Withoon's house; the divorce had been on paper only. The house was spotless, but in the ashes of an incinerator behind it investigators found a three-inch glass bottle holding a drink mixed with cyanide, and more cyanide was in the console of her car. She admitted buying it and said an acquaintance had told her to mix it with drugs.
Fourteen Victims
Once Rapee's posts spread, dozens of tips came in within a day: people around Am had been dying since 2015, each death ruled sudden or natural, and most of them had lent her money. The country began calling her "Am Cyanide." Investigators confirmed fourteen murders across eight provinces between 2015 and 2023. The first, in 2015, was a 37-year-old friend who had lent her $1,500. Her gold necklace and pendant went missing, and Am later posed as executor of her estate and sold her building for $100,000. Five years later a 36-year-old woman in a savings group Am ran died after lending her $4,500, and four more deaths followed in the last months of 2020. Am used her husband's connections to set up lending circles among police officers and their wives, borrowed from them, and when they asked for repayment, offered them food or "health supplements." One survivor, Kantima Phaelsard, whose husband had been at the police academy with Withoon, lent Am $7,500. In September 2022, recovering from COVID, she took a cough medicine Am had given her and, driving to meet her, could not breathe and felt her hands stiffen. She called Am, who said she was lost and asked what she was supposed to do about it. Paramedics revived Kantima with CPR. She did not suspect the medicine until Koy's case became public.
Final Thoughts
Am had been gambling online for years on illegal loans and owed more than she could repay, and she took over $150,000 from victims through investment, lending and used-car groups. Koy had lent her $1,500. In 2022, months after the divorce, Am moved in with a loan shark named Sutthisak. Two days later, on her birthday, she gave him a pill at a gas station. He collapsed and was taken to hospital, where he regained consciousness. Am insisted on taking him home against the doctor's advice, and he died hours later. She sold his valuables at a jeweler in two visits five days apart, and Withoon came to collect her. Withoon was convicted as an accomplice and sentenced to one year and four months. Am, four months pregnant at her arrest, denied everything. Investigators interviewed more than 900 people and brought over 75 charges, including 14 counts of premeditated murder and one of attempted murder. In November 2024 she was sentenced to death for Koy's murder. She has since received a second death sentence and two life sentences, has been acquitted in three deaths where no cyanide could be proven, and still faces further trials.
Police ruled Koy's death a heart attack, said there were no cameras at the pier, and closed the case; her family and a volunteer found the footage and the killer themselves. Earlier deaths linked to the same woman had also been ruled natural. How many lives might a proper first investigation have saved?
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