Some 800,000 people were killed in Rwanda's genocide
The International Criminal Tribunal for Rwanda (ICTR) has sentenced the former head of legal affairs at the Ministry of Defence to 25 years in prison.
Lieut-Col Eprem Setako was found guilty of genocide and crimes against humanity.
He was convicted of ordering the killing of at least 30 people at a military camp in 1994.
Hutu extremists killed some 800,000 ethnic Tutsis and moderate Hutus during the 100-day genocide.
"The Chamber found that Setako ordered the killings on 25 April 1994 of 30 to 40 Tutsis at Mukamira military camp in Ruhengeri prefecture and around 10 other Tutsis there on 11 May 1994," said a statement posted on the ICTR's website.
Setako, 60, was acquitted of other charges of complicity to commit genocide, murder as a crime against humanity and pillage as a war crime.
He was arrested in the Netherlands in 2004, before being transferred to a UN facility in Arusha, Tanzania, to face the charges.
Prosecutors said he had armed and trained militiamen and ordered them to kill Tutsis in several areas.