The Cambodia National Rescue Party yesterday released evidence they say clears imprisoned opposition Senator Hong Sok Hour, presenting a webpage which, since 2013, has hosted the “fake” border treaty the lawmaker is accused of fabricating.

Yesterday, CNRP president Sam Rainsy revealed a link to the website World Khmer Radio Online, which appears to have hosted a Khmer version of the “fake” treaty since 2013.

Sok Hour was detained on August 15 for showing the treaty in a video uploaded to Rainsy’s Facebook page and faces charges for incitement and allegedly forging the document.

Rainsy said in a statement that the “allegedly forged or more likely ill-translated document” originated from an independent source and had been shared for many years on the web, proving Sok Hour had not forged it.

World Khmer Radio Online representative Suwith Changmani said he was unable to say when, or by whom, the treaty – which he hadn’t read – was uploaded.

The CNRP statement also didn’t get into who created the document, though noted historian Michael Vickery has alleged the “fake” 1979 Cambodia-Vietnam treaty – specifically Article 4, which says the countries will “dissolve” their borders – was written by former Cambodian politician and nationalist Sean Pengse prior to 2004.

However, France-based Pengse – whose comments in 2005 on Beehive Radio about the border saw station owner Mam Sonando imprisoned – yesterday denied he had fabricated any treaties.

Speaking via telephone, Pengse, head of the activist group Cambodia Border Committee, said the Khmer, English and French versions of the treaty he possessed had been passed to him by journalists.

The deputy prosecutor in Sok Hour’s case, Sieng Sok, declined to comment yesterday.

The 1979 treaty laid the preliminary groundwork for subsequent treaties concerning the still-ongoing demarcation of the eastern boundary, and was signed by present-day National Assembly President Heng Samrin – who was then head of the Vietnam-installed People’s Republic of Kampuchea.

According to the government, the original Article 4 says the countries will negotiate a treaty to delineate the boundary. The fake treaty differs, stating Cambodia and Vietnam will negotiate an agreement to “dissolve” – in Khmer, “romleay” – their borders.

However, Vickery – the author of several books on Cambodia, including Cambodia 1975-1982 – said he had first seen the altered treaty on the website of Pengse’s group in 2004, before it was removed the next year.

In an unpublished paper, Vickery claimed Pengse had made more than one “dishonest” translation of treaty documents in order to provoke hostility toward Vietnam.

Through his organisation, Pengse – a former minister in the Lon Nol regime in the 1970s – has been a fierce critic of the ruling Cambodian People’s Party’s border policy.

He argues Cambodia has lost land to Vietnam through border treaties signed in the 1980s, and a supplementary treaty agreed upon in 2005, which he labels invalid.

Members of the CNRP have long levelled similar claims, accusing the government of using charts favourable to Vietnam instead of the constitutionally mandated French Bonne maps to demarcate the border.

However Vickery rejected the entire “correct map” debate.

He said French cartographers who surveyed borders in the Indochina region before Cambodian independence in 1953 to 1954 had made objective errors, meaning distances on the map didn’t always correspond to the ground.

The “greatest mistakes” were made in the Cambodia and South Vietnam border, particularly around the Svay Rieng and Prey Veng area, he said, citing papers by French scholars Victor Delahaye and Louis Malleret.

“What must be emphasised now is that no maps, not those offered by Sam Rainsy, nor those prescribed in neither the constitution, nor those in Sihanouk’s mind when he asked the international community in 1967 to recognise Cambodia’s sovereignty within its existing borders, are accurate for the south Cambodia-Vietnam border region,” Vickery, an adjunct professor at Chiang Mai University in Thailand, said via email.

French journalist Alain Gascuel, who has studied the border issue in depth, agreed there were imperfections in the colonial charts, which were intended to map an administrative border, not an international one.

Senior Minister on Border Affairs Va Kim Hong said that although the Bonne map was not perfect, “there is no better map”.

Yesterday, Cambodia’s Ministry of Foreign Affairs released a statement after a bilateral meeting with Vietnam, saying the demarcation would be completed “as soon as possible”.