Jean Paul Bizimana, 31, was among Rwandan rebels who abducted 14 tourists and their guide as they tracked rare mountain gorillas, the judge said.
Nine of them were brutally killed with clubs and machetes. The tourists were from the US, the UK and New Zealand.
Bizimana is to be sentenced on Friday by the Kampala court.
His lawyer said he would appeal.
News updates on the endangered animals visited by Douglas Adams and Mark Carwardine for their book and radio series "Last Chance To See". With updates on the TV series featuring Stephen Fry.
GA4
Monday, January 09, 2006
MOUNTAIN GORILLAS - Rwandan guilty of tourist murders
BBC News has an update on the trial of a former Rwandan soldier, who has been found guilty of the brutal murder of eight western "mountain gorilla tourists" and a game warden in 1999.