The Cambodian government denied the findings of an annual Human Rights Watch report.
The investigation stems from a drunk driving accident that injured three people on a motorcycle.
Arbitration Council President Kong Phallack said the lower number was due to the closure of factories in the wake of the 2008 crisis.
Hun Sen was responding to concerns raised by the US lawmakers as the refugee center nears its closing date, Feb. 15.
Yoeung Baloung, a former police chief of Ratanakkiri province, was supposed to be in jail on charges related to illegal logging.
The four men were charged under Article 38 of the 1992 penal code and face up to seven years in prison if convicted.
The recent midterm elections in US Congress should serve as a good model for Cambodians on how power can be shifted smoothly.
Some NGOs say they fear the law will be used as a tool of repression against anti-government groups.
Hun Hean, the recently demoted police chief of Banteay Meanchey province is being held on suspicion of drug trafficking.
Critics say the proposed law creates tangles of red tape that could be used to attack groups that don't follow the government line.
The law will require NGOs to provide financial reports and action plans to the government.
According to officials, more than 1,600 Cambodians died in road accidents in 2010.