Chea Vichea was a powerful labor leader able to amass large rallies, his killers have never been brought to justice.
At least 20 people, including some police and military police were injured, and at least 12 people were arrested.
Chhoung Chu Ngy briefly disappeared on Thursday last week, but he appeared shaken before a press conference on Friday.
Across Asean there is a diversity of political systems and leadership, as well as wide economic gaps.
In a meeting this week both foreign ministers said they would speed up negotiations over joint development in offshore blocs.
The Thai foreign minister made his request on an official visit to Cambodia and suggested consideration of a royal pardon.
Recently, Prime Minister Hun Sen has called for the nullification of land certificates in protected natural areas in Cambodia.
The draft law has come under continued criticism from international and local NGOs, who say it will stymie their work.
The two appeared before the Court of Appeals on Wednesday, withdrawing their appeal without explanation.
Chan Cheng and a party lawyer are accused of helping a party activist, Meas Peng, wanted for questioning in a land dispute.
The National Assembly, which is dominated by the ruling Cambodian People’s Party, voted to suspend Chan Cheng’s immunity last week.
Foreign Minister Hor Namhong told reporters that Cambodia would work toward regional integration in 2015.