Cambodia's highest court has acquitted and ordered the release of two men widely believed to have been wrongfully convicted and jailed for the 2004 murder of a prominent union leader.

Chea Vichea, a vocal critic of Prime Minister Hun Sen's government, was gunned down in broad daylight at a news stand in the capital Phnom Penh - a killing decried by activists as an attempt to silence his labour union.

Days later, Born Samnang and Sok Sam Oeun were arrested and quickly jailed for 20 years each in a verdict which rights watchdogs said was based on insufficient evidence.

The pair have maintained their innocence, saying that they were framed by a group of police.

In 2008 the Supreme Court provisionally released the pair and ordered a retrial. But the Appeal Court ruled last December that there was enough proof of their guilt and confirmed the 20-year sentences.

Free at last

After an appeal hearing on Wednesday, Judge Kim Pon at the Supreme Court said the charges against the men were dropped due to insufficient evidence, and ordered them released from jail.

Now the United Nations and embassies in Phnom Penh need to demand a real investigation to find the true culprits in the killing.

Phil Robertson, Deputy director of Human Rights Watch's Asia division

"I am happy that the Supreme Court has rendered justice for me," Sok Sam Oeun told reporters.

Rights activists immediately applauded the court's ruling, but called on authorities arrest the union leader's killers.

“Born Samnang and Sok Sam Oeun were nothing but scapegoats, framed by the Cambodian authorities over the killing of trade union leader Chea Vichea. The question that remains now is: when will his real killers be brought to justice?” said Isabelle Arradon, Asia-Pacific Deputy Director at Amnesty International.

No other suspects have been arrested for the murder.

"The nightmare for scapegoats Born Samnang and Sok Sam Oeun is finally over, but their convictions without any credible evidence of guilt and years of imprisonment are an enduring black mark on the already tattered reputation of the Cambodian judiciary," Phil Robertson, deputy director of the New York-based Human Rights Watch's Asia division, told Reuters.

"Now the United Nations and embassies in Phnom Penh need to demand a real investigation to find the true culprits in the killing."

The Office of the United Nations High Commissioner for Human Rights also welcomed the acquittal and called for a "full investigation" into the murder.

Symbol of impunity

Chea Vichea founded the Free Trade Union of Workers of the Kingdom of Cambodia along with opposition leader Sam Rainsy, and organised many protests for the rights of garment workers.

A statue of him was unveiled in May in a rare public tribute to a champion of worker rights in the impoverished kingdom.

Campaigners say his murder is a symbol of the kingdom's culture of impunity for powerful interest groups determined to muzzle dissent.

Source: Agencies