On April 14, 2023, Siriporn Khanwong, known as Koy, drove with a friend to the Mae Klong River in Ratchaburi province, west of Bangkok, to release fish as an act of Buddhist merit-making. They stopped to eat. Siriporn collapsed and died on the riverbank, and the autopsy found cyanide. Her bag, her money and her phone were missing. Eleven days later, on April 25, police arrested the friend, Sararat Rangsiwuthaporn, thirty-six, the wife of a police lieutenant colonel, who was four months pregnant; she later miscarried in custody. Once investigators knew what they were looking for, they went back through unexplained deaths among the people she knew and found a pattern that reached back to 2015.
Sararat was born on March 12, 1987. Her husband at the time, Police Lieutenant Colonel Withoon Rangsiwuthaporn, was a senior officer, and she moved in comfortable circles, but by the time of her arrest she had run up heavy debts on credit cards and online gambling. The Thai press gave her the name Am Cyanide, from her nickname and her poison. The deputy national police chief, Surachate Hakparn, described the method in a sentence: she borrowed money from people she knew because she had so much credit card debt, and if they asked for it back, she killed them. Some of the loans ran to 300,000 baht, about nine thousand dollars.
The pattern the police described was a meeting with a creditor or an investor, a promise to repay, a capsule or a dish offered as medicine or food, and a collapse. Fifteen people in seven provinces were given the poison between 2015 and 2023, and one survived. Investigators recovered fingerprints and other evidence from her car, and she was found with a bottle of cyanide at her arrest. On June 30, 2023, police forwarded more than eighty charges to prosecutors, among them premeditated murder, attempted murder, theft causing death and forgery, which they called a record in Thai criminal history. Surachate told reporters that even Jack the Ripper had not killed so many, and the government tightened controls on access to cyanide.
The prosecutions have run one case at a time. On November 20, 2024, the Criminal Court in Bangkok convicted her of Siriporn's murder, of robbing her of property worth more than four thousand dollars and of adulterating food so as to cause death, and sentenced her to death; she did not testify. In February 2026 she was convicted of the murder of the police officer Nipa Saenchan, and on April 30, 2026, of the murder of Police Captain Sukanda Wimolman, poisoned in Khon Kaen on August 9, 2022. In both cases the court pronounced death and reduced it to life because her testimony had been of some use to the proceedings.
The court also acquitted her three times: of the murder of the engineer Nittaya Kaewbuppha on March 11, 2026, of the murder of the vegetable seller Rosjarin Nilnoi on July 21, 2026, and of a sixth charge on August 4, 2026, finding in each that nobody had seen her give the poison and that the evidence did not close the gap. On August 25, 2026, she was sentenced to death for the murder of Darinee Thepthawee, thirty-four, a creditor, whom prosecutors said she had given food laced with potassium cyanide in Nakhon Pathom in December 2020; toxicologists at Siriraj Hospital found that the poison had destroyed the heart, lungs and liver, and the court ruled that she had planned the killing to clear a debt she could not pay.
The eighth judgment came on September 22, 2026. Chantharat Wongkraisin, forty-three, known as Jum, had invested money in a lending scheme Sararat ran. On August 9, 2022, the court found, Sararat ordered a jar of cyanide; she arranged to meet Chantharat on August 12 to repay the money with interest and bring her medicine for long Covid, then put the meeting off when she learned the victim's husband and child would be home for the holiday, and met her instead on August 15 at a gas station near her house in Phetchaburi. Chantharat was found dead at home afterward. Telephone records and money-transfer slips carried the case, which rested on circumstantial evidence, and the court sentenced Sararat to death and ordered her to pay the widower 60,000 baht with interest. It was her third standing death sentence. Her lawyers said they would appeal, and death sentences in Thailand are reviewed on appeal in any event.
Seven cases remain. The names in the police file include Policewoman Captain Kanda Torai, the teacher Maneerat Pojanat, Pusadee Samboonmee, Sawittree Budsrirak of Mukdahan and a former boyfriend of Sararat's, Sutthisak Poonkwan; one other case, over the death of Monthathip Khao-in in Bangkok in 2016, was dismissed, and the attempted-murder case of Kantima Paesa-ard, the one person who survived, was set for trial on November 25, 2026. Much of the international coverage reported the first verdict as a conviction for fourteen murders. It was not, and the arithmetic has not simplified since: five murders proved, three not proved, and seven still to be heard. Sararat has denied the charges throughout.
Two people were prosecuted alongside her. Her former husband was sentenced to sixteen months for concealing evidence and helping her evade arrest, and was separately accused of assisting in the death of Sutthisak Poonkwan; her lawyer, Thanicha Aeksuwannawat, was accused of helping to hide evidence. Both denied the allegations. What held Thailand's attention was not only the number of deaths. The victims were her friends, the deaths had passed as natural for eight years, and the woman accused of them was married to a police officer. It is the largest poisoning case ever prosecuted in the country.