Approximately 20,000 protestors from across the country rallied on Phnom Penh streets on Sunday holding banners, graphic images, photographs of prisoners, skulls, and torture instruments from S-21, demanding that Kem Sokha apologize for the speech he made in which he claimed that the exhibitions at Tuol Sleng genocide museum were "staged".

The protest came after a ten-day ultimatum given to Kem Sokha, lawmaker and acting president of the opposition Cambodia National Rescue Party (CNRP), expired without the requested apology. He was given ten days to apologize to the survivors. Kem Sokha refused, saying that his recorded speech was cut and edited out of context by the government.

Kem Sokha has denied from the beginning that he made the comments, claiming that such charges were politically motivated and organized in the run-up to the national election.

"My speech has been modified to manipulate the meaning and intention of the whole speech. I never stated that S-21 prison is artificial…the victims, who were tortured and murdered in S-21, were framed by the Khmer Rouge through arrangement of fake evidence to make them guilty and receive punishments," said Kem Sokha in a press conference at CNRP Headquarters on May 29, 2013.

When asked what exactly he said about S-21, Kem Sokha replied that he did not remember exactly because he had given so many talks in public forums since 2002.

Trucks carrying protestors with banners pouring into Phnom Penh's Democratic Park marked one of the biggest protests against a single individual in recent history. The protests were staged not only in Phnom Penh but also in other provinces. Two days earlier, Cambodia's parliament approved a bill which would require that those who are found guilty of denying crimes committed by the Khmer Rouge be given jail sentences of up to six months or required to pay fines up to $1,000.

Marching in the street was Chum Mey, who is a survivor of S-21. He expressed his strong anger against Kem Sokha for refusing to apologize to survivors who suffered from the Khmer Rouge regime. Chum Mey said that Kem Sokha is a coward. One banner reads "the souls of the deceased victims of Tuol Sleng prison are demanding Kem Sokha's apology." Another banner reads "Kem Sokha is more cowardly than Duch." Duch whose full name is Kaing Guek Eav admitted crimes he committed at S-21 during the Khmer Rouge regime and was sentenced to life in prison last year.

The protestors were mostly survivors of the Democratic Kampuchea regime and students who, although born after the regime ended, had learned from their parents and at school that crimes were committed at Tuol Sleng by the Khmer Rouge between 1975 and 1979.

At around noon, 5,000 protestors continued their march to CNRP Headquarters near the Royal University of Phnom Penh to hand over their petitions. Representative of the Party came to receive them.

Heng Vicheth, a government official who witnessed the protests, said that such a demonstration of public opinion could not be ignored and that as a public figure Kem Sokha needs to be more responsible for what he says.

Lay Sonita, an NGO staff member who drove her car past the protest also expressed her concerns about youth who participated in the protest. However, Sonita felt positive that "this protest would encourage the younger generation to learn more about the history of the Khmer Rouge."

Phong Bunna agreed with Sonita, saying said that students who had never been to Tuol Sleng museum should visit the museum to learn on the ground and for themselves what happened during the Khmer Rouge period.