for minor or political crimes, began with a warning from the Angkar, the government of Cambodia under the regime. People receiving more than two warnings were sent for "re-education," which meant near-certain death. People were often encouraged to confess to Angkar their "pre-revolutionary lifestyles and crimes" (which usually included some kind of free-market activity; having had contact with a foreign source, such as a U.S. missionary, international relief or government agency; or contact with any foreigner or with the outside world at all), being told that Angkar would forgive them and "wipe the slate clean." They were then taken away to a place such as Tuol Sleng or Choeung Ek for torture and/or execution. The executed were buried in mass graves. In order to save ammunition, the executions were often carried out using poison or improvised weapons such as sharpened bamboo sticks, hammers, machetes and axes. Inside the Buddhist Memorial Stupa at Choeung Ek, there is evidence of bayonets, knives, wooden clubs, hoes for farming and curved scythes being used to kill victims, with images of skulls, damaged by these implements, as evidence. In some cases the children and infants of adult victims were killed by having their heads bashed against the trunks of Chankiri trees, and then were thrown into the pits alongside their parents. The rationale was "to stop them growing up and taking revenge for their parents' deaths." Some victims were required to dig their own graves; their weakness often meant that they were unable to dig very deep. The soldiers who carried out the executions were mostly young men or women from peasant families. Prosecution for crimes against humanity In 1997 the Cambodian government asked for the UN's assistance in setting up a genocide tribunal. It took nine years to agree to the shape and structure of the court—a hybrid of Cambodian and international laws—before the judges were sworn in, in 2006. The investigating judges were presented with the names of five possible suspects by the prosecution on 18 July 2007. On 19 September 2007 Nuon Chea, second in command of the Khmer Rouge and its most senior surviving member, was charged with war crimes and crimes against humanity. He faced Cambodian and foreign judges at the special genocide tribunal and was convicted on 7 August 2014 and received a life sentence. On 26 July 2010 Kang Kek Iew (aka Comrade Duch), director of the S-21