* Rights groups cry foul, say pair were framed
* Cambodia drawing flak for rights record, judiciary
PHNOM PENH, Dec 27 (Reuters) - A Cambodian court ordered the return to prison on Thursday of two men seen by rights groups as scapegoats for the murder of a top unionist, the latest controversial ruling in a country chided for its low judicial standards.
The Appeals Court upheld a lower court's handing down of 20-year jail terms for Born Samnang and Sok Sam Oeun for the 2004 killing of Free Trade Union (FTU) leader Chea Vichea, despite weak evidence and activist claims the pair were framed.
Following a public outcry, the Supreme Court released the two on bail in 2008 after three years in jail to allow further investigation. The Appeals Court on Thursday made no mention of any new evidence against them.
"Please help me, this is very unjust," Born Samnang shouted as he was taken away by police. He wept and said he would seek help from King Norodom Sihamoni to clear his name.
Cambodia's positive image among investors as one of Asia's most promising emerging economies and a cheaper alternative to China is being dented by allegations of rampant rights abuses and political interference in the judiciary to silence dissent or allow well-connected figures to walk free.
An alliance of 19 local organisations, activists and rights groups condemned the ruling and said the judges chose to "systematically dismiss and ignore evidence and testimonies in favour of the two".
It issued a statement saying both men had credible alibis and a newspaper seller - the only witness to Chea Vichea's murder - and the former lead police investigator had said Born Samnang and Sok Sam Oeun were not the killers.
"This morning's verdict has left us speechless," said Moeun Tola of the Cambodia Legal Education Centre. "The Appeals Court decision defies any sense of justice and rule of law."
Violence against union leaders is not uncommon in Cambodia and activists say scapegoats have been found to ensure those instigating the attacks go unpunished.
As Cambodia's $4.2 billion garment manufacturing sector grows, unions and workers are becoming increasingly emboldened, holding protests and strikes over pay and working conditions.
Rights groups were incensed last week when a local politician connected with the ruling party was cleared by a court of firing bullets into a crowd of striking factory workers earlier this year, wounding three women.
Chea Mony, the current FTU president and brother of the late Chea Vichea, said he was shocked by Thursday's ruling and criticised the authorities for failing to bring the real culprits to justice.
"We have not seen any light of justice at all in this case," Chea Mony told Reuters. "The court is well aware of what's going on and that it lacks its independence."