Im Chaem did not say who had asked her to retire, but she said her name was withdrawn from a candidate’s list.
Duch told the court Nuon Chea ordered him to execute prisoners at the facility, known to the Khmer Rouge as S-21.
The filmmakers will receive the award May 21 in New York.
A tribunal spokesman said the list of witnesses who will testify remains confidential.
Thaksin himself will attend for a Buddhist ceremony, as Thais and Cambodians celebrate the New Year.
The group rates Cambodia the 20th-most corrupt nation in the world, putting it in the company of Guinea, Kyrgyzstan and Yemen.
Defense attorneys have said that the woes over the two cases highlight corruption in the tribunal’s judicial process.
Several Asean members, notably the Philippines and Vietnam, have overlapping claims to the sea with China and Taiwan.
China claims ownership of much of the South China Sea, along with four ASEAN states, including the Philippines.
Host President Hun Sen focused on economic issues in his opening remarks Tuesday.
Burmese President Thein Sein told reporters in Phnom Penh Tuesday the elections had been a success.