The court in Bangkok found Sararat Rangsiwuthaporn, 36, guilty of putting poison in a wealthy friend’s food and drink while they were on a trip last year.
Relatives of the friend refused to accept she died of natural causes and an autopsy found traces of cyanide in her body. Police arrested Sararat and uncovered other similar deaths going back to 2015. One person she allegedly targeted survived.
Police say Sararat, dubbed Am Cyanide by Thai media, had a gambling addiction and targeted friends she owed money to, then stole their jewellery and valuables.
Sararat travelled with her friend Siriporn Khanwong, 32, to Ratchaburi province, west of Bangkok in April 2023, where they took part in a Buddhist protection ritual at a river, police said.
Siriporn collapsed and died after a meal with Sararat, who made no effort to help her, investigators said.
Traces of cyanide were found in Siriporn’s body and her phone, money and bags were missing when she was found, police said.
“You got justice, my child. Today, there is justice in this world,” Siriporn’s mother, Thongpin Kiatchanasiri, said in front of the courtroom, as she held a photo of her daughter.
Thongpin said that out of anger, she could not stand to look at Sararat, who she said was smiling when the sentence was being read. Sararat pleaded not guilty to the charges against her.
Her former husband, an ex-police officer, and her lawyer, were handed prison terms of one year and four months, and two years respectively, for hiding evidence to help her evade prosecution. They had also pleaded not guilty before Wednesday’s sentencing.
The ex-husband, Vitoon Rangsiwuthaporn, gave himself up last year. Police said he most likely helped Sararat poison an ex-boyfriend, Suthisak Poonkwan.
Sararat was also ordered to pay Siriporn’s family two million baht ($57,667; £45,446) in compensation.
Cyanide starves the body’s cells of oxygen, which can induce heart attacks. Early symptoms include dizziness, shortness of breath and vomiting.