The four men were charged under Article 38 of the 1992 penal code and face up to seven years in prison if convicted.
Protesters had prepared a letter for the embassy, but embassy officials would not accept it.
Rapp, who staid in Cambodia Thursday through Sunday, said his visit had convinced him the investigations will go forward.
The recent midterm elections in US Congress should serve as a good model for Cambodians on how power can be shifted smoothly.
Government ministry officials have until March to add up their worth and send it to anti-corruption authorities.
Four seniors leaders—Nuon Chea, Khieu Samphan, Ieng Sary and Ieng Thirith—are awaiting trial for atrocity crimes, including genocide.
Some NGOs say they fear the law will be used as a tool of repression against anti-government groups.
Thai lawmaker Panich Vikitsreth and Narumol Jitrawarattana, were released after they paid their bail, approximately at $250 each.
The seven Thais, including a member of parliament, are facing a potential prison sentence of 18 months, for illegal entry into Cambodia.
Cambodia is hoping to produce 1 million tons for rice for export by 2015.
Moeuk Dara, secretary-general of the the National Authority to Combat Drugs, was put under arrest by the Ministry of Interior.
Around 2,120 victims who have registered as civil party complainants have been accepted from more than 4,000 applications.