Ex-head of state Khieu Samphan, chief ideologue Nuon Chea face genocide charges at the trial that begins Wednesday in Phnom Penh.
Officials say crudely built, unmanned aircraft was equipped with basic camera containing about 200 aerial photographs, including some taken from directly above presidential Blue House.
The discord was widely attributed to political pressure from China, which would rather deal separately with the five nations with which it has maritime disputes.
