The Anti-Corruption Unit (ACU) is taking action on a corruption complaint against opposition leader Kem Sokha for allegedly promising property and cash to purported mistresses in leaked audio recordings, the body’s director said yesterday, after declaring experts had verified the tapes as genuine.

ACU President Om Yentieng spoke following a three-hour meeting at the unit’s headquarters.

During the press conference, it emerged that between 30 and 40 ACU officials had been assigned to work “day and night” to confirm it was the Cambodian National Rescue Party acting president’s voice on the 34 tapes, released via social media earlier this month.

Yentieng said the verification gave him grounds to unseal Sokha’s confidential declaration of assets – an extremely rare occurrence – and investigate the lawmaker’s alleged pledge to provide $4,000 for one mistress and a two-bedroom house for another.

“Even if the house that he bought for [his mistress] is declared in his wealth declaration, where did he get the money from? This is the point that requires investigation,” Yentieng said.

“Who has the authority to open the envelope of wealth declaration? It’s me, Om Yentieng.”

Yentieng said Sokha was being probed under Article 36 of the Anti-Corruption Code, concerning illicit enrichment, defined as an unexplainable increase in an individual’s wealth compared with their legal income.

Under the law, asset declarations – required by lawmakers, high-ranking public officials and military officers every two years – are kept confidential unless the ACU president deems it necessary for an investigation.

Sokha has lodged declarations in 2011, 2013 and 2015. Despite repeated calls for transparency, rarely, if ever, has the ACU unsealed asset declarations, San Chey, director of the Affiliated Network for Social Accountability, noted yesterday.

Government spokesman Phay Siphan, however, maintained at least two policemen’s asset declarations had been unsealed during previous corruption proceedings, though could not provide further details of those cases.

Yentieng’s swift action in this instance contrasts starkly with years of inaction on pleas to probe the glaring discrepancies between the multimillion-dollar palatial homes and luxury cars of numerous government officials and their modest state salaries.

“We hope that the ACU will take the same measures for high-ranking government officials surrounded by hints and suspicions of corruption,” Transparency International executive director Kol Preap said yesterday.

The covertly recorded conversations have also raised questions about whether Sokha’s phone was tapped.

Salon worker Khom Chandaraty, known by her Facebook name “Mon Srey”, was identified as the voice in some of the clips, but has denied being Sokha’s mistress.

Chea Sam Ath, director of the ACU forensics examination department, said between 30 and 40 officials worked to authenticate the tapes, producing a 63-page report detailing their findings.

In a “four-stage process” they compared the leaked clips to audio of Sokha speaking on Voice of America radio, he said, adding the “faint adult voices” spoke with the same “medium” frequency and regional accent.

“In the audio, which is used as the sample, there are many of same words [used] and it matches the voice of Kem Sokha. It is the same person,” Sam Ath said.

Yesterday, legal expert Sok Sam Oeun pointed out that even if it were Sokha on the tape, references to gifts did not constitute evidence of their existence.

“If they have not yet found the house and not yet found any record of the money Kem Sokha gave to the girl, they should not rush to open the property declarations,” Samoeun said.

The corruption complaint was lodged by a group of students, who deny they have political affiliations but refuse to discuss their background for safety reasons, they claim.

Since the tapes emerged, the group has led a crusade against Sokha, who, together with the CNRP, has refused to be drawn into responding directly and yesterday were unreachable for comment.

The students have petitioned the National Assembly and crashed CNRP events.

“The answers that have been provided are satisfactory, now for the next step, it is up to the ACU’s procedures whether they take legal action against Kem Sokha,” the group’s leader Srey Chamroeun said yesterday.

Separately, anti-terror police are probing a defamation claim arising from the recordings, lodged by social media personality Thy Sovantha.

The Cambodian People’s Party and its leader, Prime Minister Hun Sen, have rejected claims that they are behind a “dirty tricks” campaign to smear Sokha.

Political observer Ou Virak said “whole process” smacked of political motivation.

“It’s more than just double standards, [the investigation] is a political decision and the ACU is the political tool,” Virak said.

“The justification for the investigation is lacking . . . If you look at the accusations and the tapes, it just doesn’t add up.”