More than 1,000 of 4,000 families have already been evicted or have moved from Boeung Kak lake area.
Richardson's visit follows a high-profile trip by US Secretary of State Hillary Clinton in November.
Members of the Thailand Patriot Network gathered in front of the Cambodian Embassy to call for the release of the group.
Meanwhile, the National Election Committee has been accused of weak enforcement of the Election law.
The reporters killed include those who supported the opposition parties, as well as the pro-government newspaper Koh Santepheap.
The charges carry a sentence of three to six months in jail and a fine of up to $500.
In a statement to the Assembly, Prime Minister Hun Sen said Cambodia had a 30-fold difference in trade imbalance.
Opposition members did not support this loan initiative because it was not clearly allocated.
The new penal code law, passed last year, has been made effective throughout the country since Nov. 12.
Cambodia goes to the polls every five years, first in national elections and then in parliamentary elections.