But a government committee said the bridge disaster was not the fault of any body or agency.
Ou Virak, president of the center, said the victims have the right “to find out the facts” of the incident.
Some 2,700 people from 14 provinces contributed corruption complaints earlier this year.
In a joint statement by 66 NGOs last week, groups said they wanted to contribute meaningful input to the draft law.
Chea Vichea, a widely popular labor leader, was shot to death in February 2004.
A leading Khmer Rouge tribunal monitor said Monday he was optimistic about the UN-backed court.
Suu Kyi was released on Saturday, imprisoned or under house arrest for most of the last 20 years.
Meanwhile, the tribunal continues to face funding woes, as donors wait for a completion strategy before deciding on the amount of funds.
Some were upset by the lack of provisions within Asean and its commission on key rights freedoms.
Activists say a general atmosphere of impunity still prevail, while police continue to seek bribes or commit abuses.