A shocking crime in central Bangkok: a 21-year-old woman with a mental illness repeatedly stabbed her 23-year-old elder sister over 50 times, causing her death inside their luxury condo in Sathorn. Police preliminary investigation indicates the motive was resentment after the elder sister secretly checked the younger sister's phone and revealed her secret of flushing medication down the toilet to their parents, sparking the attack.
At 11:08 a.m. on 19 June 2026, Police Lieutenant Akrawit Nuanta, Deputy Inspector of Yannawa Police Station, received a report of a murder at a luxury condo in Sathorn, Bangkok. He informed his superiors and proceeded to investigate with Police Major General Chaikrit Pho-a, Commander of Metropolitan Police Division 6; Police Colonel Narit Pratthanaporn, Deputy Commander of Division 6; Police Colonel Cherdsak Rodkhem; Police Colonel Phansa Amornpitak, Chief of Yannawa Police Station; the investigative team of Yannawa Police; forensic officers; medical examiners from Police General Hospital; and volunteers from the Poh Teck Tung Foundation.
The scene was a 24-story high-rise building, with the incident occurring on the 17th floor inside the condo unit, which consists of three rooms: two bedrooms and a living room. In the room of Miss Siw Hui (surname withheld), age 21, the body of Miss Siw Chong (surname withheld), age 23, the elder sister, was found curled up at the foot of the bed near the window, wearing a pink nightgown. She had stab wounds from a knife: 3 in the chest, 5 in the neck, 6 on the hands, 5 on the back, and over 10 on the right arm, totaling more than 50 wounds. Blood was splattered throughout the room, and the blackout curtains were soaked in blood.
During questioning, Mr. Cheng (surname withheld), 69, the victim's father and first to discover the body, said that four family members lived in the unit: himself, his wife, and their two daughters. The victim had recently graduated from university and had just attended her graduation ceremony. The perpetrator was a second-year university student in Chiang Mai province but had recently taken a leave of absence due to mental health issues and was undergoing treatment at a psychiatric hospital on Ratchaphruek Road in Nonthaburi province.
Before the incident at about 8:30 a.m., the father and his wife went to the market near Saint Louis. Around 9:30 a.m., Miss Siw Hui called his wife to pick her up to go ice skating, telling her not to come upstairs but that she would wait downstairs. When the wife arrived, she took the younger daughter out and asked where the elder sister was. Miss Siw Hui said she was still in bed. The wife then called the elder sister's phone, but she did not answer, so the father tried calling several times with no response. Concerned, he drove back home and went upstairs to Miss Siw Hui's room, where he found the tragic scene.
The cause was that Miss Siw Hui had mental health issues and was prescribed medication. However, her symptoms worsened over time. Two or three days earlier, the father took her to the doctor again, who said the symptoms indicated medication withdrawal. The father did not initially believe she had stopped taking her medicine because the supply matched the days prescribed. When pressed, she admitted to having flushed all her medication down the toilet long ago. The doctor then prescribed new medication, instructing the father to administer it daily, but before treatment could take effect, the tragic event occurred.
Police then contacted Miss Siw Hui's mother to bring her back to the condo where the incident happened. Officers waited outside to take her into custody. Miss Siw Hui appeared calm. Police brought her upstairs to the crime scene and questioned her about the knife. She revealed she had hidden the weapon—a kitchen knife approximately 30 cm long—on a bookshelf in the living room.
During interrogation, Miss Siw Hui claimed she was angry at her elder sister for secretly checking her phone and revealing the secret of discarding medication to their parents. She said she bought the knife at a supermarket beforehand and took advantage of the moment when their parents were out to carry out the attack.
Initially, authorities took the suspect and the evidence to the investigator, charged her with premeditated murder, and handed the victim’s body to volunteers from the Poh Teck Tung Foundation to transport to the Forensic Institute at Police General Hospital for a detailed autopsy.