A US congressman warned this week the killers of opposition journalist Khim Sambor should be brought to justice.
"Whoever killed him needs to be held accountable," said Representative Christopher Smith, a Republican. If those who did the killing were under instruction from an official, "that individual needs to be held accountable as well."
Kim Sambor was gunned down with his son on a Phnom Penh street July 11, two weeks ahead of national elections. No one has been arrested in the murder, which opposition reporters said created a chilling effect on their coverage of the government and the ruling Cambodian People's Party.
The Cambodian people should not have to tolerate such unresolved murders, Smith said, calling on Prime Minister Hun Sen to "do everything to cooperate" and go "wherever" the investigation leads.
The US said earlier this week the FBI had been asked to help investigate the murder.
Smith, who works closely with human rights issues, said public officials should be open to criticism, "because that's how you hold them accountable."
"I don't like it when I am criticized, but I know it's part of a larger and very important principle," he said.
Twelve journalists have been killed in Cambodia since 1994, but no suspects have been arrested in the crimes.