Sitanan Satsaksit, the sister of pro-democracy activist Wanchalearm Satsaksit, who was abducted in Phnom Penh, arrived in the Cambodian capital earlier this month, together with legal aides, to seek answers about her brother's disappearance.
Ms Sitanan has received a summons from an investigative judge in Phnom Penh about her brother's disappearance. There will be a closed-door hearing in court on the matter on Dec 8.
Mr Wanchalearm, who was living in exile, was last seen on June 4 near his apartment in the city's Chroy Changvar district, according to local media.
VOA Khmer reported that "CCTV footage from [that day] shows a black SUV speeding away from Wanchalearm's home."
He has not been seen since.
Mr Wanchalearm was a critic of the military regime; he fled to Cambodia in 2014 after failing to respond to a summons issued to political dissidents.
In Cambodia, the 38-year-old activist continued his crusade against Prime Minister Prayut Chan-o-cha's government.
Reports said Mr Wanchalearm, who was affiliated to the United Front for Democracy against Dictatorship (the red shirts), ran a Facebook page while in exile, posting satirical content criticising the Thai government.
In 2018, Thai authorities issued another arrest warrant, this time for violating the 2016 Computer Crime Act.
On May 13, Thai police reportedly visited Mr Wanchalearm's home in Ubon Ratchathani asking about his whereabouts. After hearing about it, he took to Facebook to mock the police that came to his house.
Ms Sitanan believes that last post "might have been the final straw".
She says her brother was taken by Thai operatives in Phnom Penh, a notion dismissed by the authorities in Thailand.
Cambodian authorities initially denied Mr Wanchalearm was even in the country during the time of his disappearance, despite the CCTV footage and eyewitness accounts, but they have since changed their stance.
The media speculates the denial stems from relations between Bangkok and Phnom Penh.
The United Nations has documented 80 cases of suspected enforced disappearance and torture in Thailand over the past 15 years. Since the coup, nearly a dozen dissidents in exile have gone missing.
The United Nations Human Rights Office of the High Commissioner (OHCHR) says an enforced disappearance is defined by three cumulative elements: Deprivation of liberty against the will of the person; involvement of government officials, at least by acquiescence; and refusal to acknowledge the deprivation of liberty or concealment of the fate or whereabouts of the disappeared person.
In Dec 2018, there were reports that well-known activist Surachai Danwattananusorn and two other dissidents disappeared while in hiding in Laos. A few days later, two dismembered bodies were found afloat in the Mekong river on the Thai-Lao border.
It's believed the bodies were those of Chatchan Bupphawan, or Comrade Phuchana, and Kraidej Luelert, or Comrade Kasalong, who were with Surachai.
The gruesome findings have put the Thai state in hot water, yet it has never come clean about the issue.
Mr Wanchalearm's abduction on June 4 prompted human right advocates to ramp up their efforts in pushing a bill on enforced disappearance, a long-overdue legal mechanism to address this debacle.
As pressure mounted, the Prayut government eventually endorsed the bill on June 23 and sent it to parliament for vetting.
Thailand, as a signatory state to the International Convention for the Protection of all Persons from Enforced Disappearance (ICPPED), is required to issue this law if it is to ratify the convention.
Cambodia, however, leads by one step ahead as it is a party to the convention.
This may explain why Cambodia cannot sit idle on Mr Wanchalearm's disappearance. Clearly, the neighbouring country is obligated under international law to investigate cases of enforced disappearances.
Mr Wanchalearm's alleged enforced disappearance has also fuelled anger among activists in Thailand, who took up the case. They say concerned agencies are not active enough.
Thai authorities in Phnom Penh should do more in assisting Ms Sitanan find out exactly what happened to her brother. They can at least provide legal aid to assist in Ms Sitanan's mission.
Although he is a critic of the Thai state, Mr Wanchalearm is a Thai citizen who has the right to state protection.
At the same time, parliament should speed up and endorse the enforced disappearance bill so the kingdom can go ahead and ratify the convention, as a responsible member of the UN should do.