The sister of a Thai pro-democracy activist who rights groups say was abducted by unknown gunmen in Cambodia called on Friday for authorities to solve the case after holding a Buddhist prayer ceremony to mark six months since his disappearance.
Wanchalearm Satsaksit, 37, was bundled into a vehicle in front of his Phnom Penh apartment in June, New York-based Human Rights Watch said. Cambodian police have previously said they were unaware a kidnapping had taken place.
During the brief ceremony outside Wanchalearm's apartment, Buddhist monks chanted and scattered sacred water.
"We do not know the perpetrator; however, it is the duty and responsibility of authorities both in Cambodia and Thailand to find the truth," Wanchalearm's sister, Sitanun Satsaksit, told reporters after the ceremony.
Wanchalearm was speaking on his mobile phone to Sitanun when he was abducted, the elder sister has said previously.
Sitanun said the family still hoped to be reunited with their brother but said the response of authorities in both countries had not been sufficient.
Sitanun is due to appear at a hearing about the case in a Phnom Penh court on Tuesday, where she plans to submit photographs and videos to show that her brother was in the city at the time of his alleged abduction.
Cambodian national police spokesperson Chhay Kim Khoeun, who had previously said police were unaware of the incident, declined to comment on Friday.
In a statement, Thailand's embassy in Phnom Penh said it was following the case but could not provide specific comment at this time since "the case is currently under legal process."
The embassy said it was closely cooperating with Cambodian authorities and would continue to provide assistance to Wanchalearm's family.
At least eight other Thai activists who fled the country after a 2014 military coup have disappeared from Laos, Cambodia and Vietnam, with some later found dead.
Thai authorities have said they had nothing to do with the disappearances.