Lim Kimya, an ex-lawmaker for the dissolved Cambodia National Rescue Party (CNRP), was gunned down on Tuesday by a motorcyclist as he arrived in Bangkok by bus from Cambodia with his French wife.
Cambodian opposition figures have accused the country’s powerful former leader Hun Sen of ordering the shooting.
A Cambodian government spokesman denied the allegations.
France has condemned the killing of Lim Kimya, who also held French citizenship.
Police in Cambodia said they arrested the suspected shooter on Wednesday, and Thailand has requested his return.
They named the suspect as Ekkalak Pheanoi, although some Thai media called him Ekkalak Paenoi and said he was a former Thai marine.
“We have sent him to Thai authorities this morning,” Cambodian National Police spokesman Chhay Kim Khoeun told AFP.
Thai state broadcaster ThaiPBS said police were waiting to receive the suspect at the border on Saturday morning.
Scores of Cambodian opposition activists have fled to Thailand in recent years to avoid alleged repression at home. Some were arrested and deported back to the country.
Hun Sen ruled Cambodia with an iron fist for nearly four decades, with rights groups accusing him of using the legal system to crush opposition to his rule.
He stepped down and handed power to his son Hun Manet in 2023, but is still seen as a major power in the kingdom.
© 2025 AFP