premise: He added that UN officials would investigate the claims that local people had been killed by the refugees. At the end of last month, several villagers were killed near refugee camps, sparking the looting of several UN World Food Programme trucks in retaliation.
  Between 80,000 and 100,000 Hutu refugees have been sheltering in camps south of Kisangani, which was taken on March 15 by Zairean rebels fighting the regime of President Mobutu Sese Seko.
  They had fled westwards from camps near the Rwandan border as the rebels swept across the eastern half of the country, taking a string of key towns, and took refuge in tropical forests where relief workers could not get aid to them.
  The UNHCR had planned on Friday to start a huge airlift operation to help the refugees on their way back to Rwanda, but this was delayed at least until Saturday.
   What sparked the looting of several UN World Food Programme trucks?
hypothesis: relief workers could not get aid to them