Nirut Sonkhamhan was born on August 5, 1969, in the Nong Kung Si district of Kalasin province, Thailand. When he was ten years old, he moved with his father to the city of Songkhla. Nirut lived in Songkhla until he turned 25 years old. At that point, he relocated to a village called Khok Krua. In Khok Krua, Nirut got married and started his own family. He found a job as a taxi driver.

He used a specific method to carry out his crimes. Sonkhamhan would hire taxi drivers to help him move items to different locations. While riding in the taxi, he would stop at a gas station to buy coffee. He would then poison the coffee with pesticide.

His first known victim was 67-year-old Yupin Jeonkhem, whose body was found on January 11, 2011. It was discovered floating in the Lampao Dam and weighed down with cement blocks. Police found fingerprints near her home, which led them to issue an arrest warrant for Sonkhamhan.

Later, in March 2011, Sonkhamhan poisoned Montree Kalam, who luckily survived. He continued his crimes, poisoning Nairob Prathon in Surat Thani. After that, he dumped Prathon's body in a palm plantation and sold the vehicle he used. In January 2012, he poisoned a man named Watchara Suebchuea and discarded his body off a bridge, but this body was never found.

Sonkhamhan also attempted to poison a taxi driver named Charoen Daranoi. However, Daranoi recognized the poisoning and escaped the situation. At the end of January 2012, he poisoned another victim, Paitoon Pattalapho, whose body he left at a sugarcane plantation, thinking he was dead, but Pattalapho survived.

In the following months, he poisoned and killed three other victims. Julsil Salangsing's body was discovered in Tha Sae district. He also brought his wife along when he killed Chamnong Srirachat, dumping the body in a grove near a canal in Chumphon district. His last known victim was Somsak Srichampa, found along the Petchkasem Road in Prachuap Khiri Khan on April 9, 2012.

Sonkhamhan was eventually caught following the review of CCTV footage from the victims' last known locations and a stolen car linked to one of the murders. He was arrested on April 16, 2012, in a hotel room. After his arrest, he was held in solitary confinement. On April 17, he attempted to take his own life using an electric cord but was saved by prison guards. The next day, he managed to harm himself again using a piece of his T-shirt. Despite attempts to resuscitate him, he did not survive.