NAIROBI, Kenya— Ethiopia’s former Marxist dictator Mengistu Haile Mariam was yesterday convicted of genocide by a court in Addis Ababa after a 12-year trial.

The 69-year-old was tried in absentia because he fled to Zimbabwe in 1991 where he lives in luxurious exile in a suburb of Harare, the capital. Robert Mugabe has said he is a “refugee” and has refused to extradite him to Ethiopia.

Along with 72 key associates, Mr. Mengistu was accused of genocide, illegal imprisonment, and abuse of power for leading a series of blood-soaked purges against political opponents during the “Red Terror” of 1977 and 1978.

No one knows how many died, but the prosecution estimated that 2,000 were killed in the two-year campaign.

During his 17-year rule, up to 1.5 million people were killed, tortured, or detained by henchmen from his Derg, or “committee.”

“Members of the Derg who are present in court today and those who are being tried in absentia have conspired to destroy a political group and kill people with impunity,” presiding Judge Medhen Kiros said in his ruling yesterday.

The guilty verdict — a rarity in Africa where former tyrants seldom face prosecution — carries the death sentence, but Mr. Mengistu is likely to live out his days in comfort.

The court began its hearings in 1994 and has since convicted 1,018 people despite difficulties collecting evidence and the deaths of dozens of witnesses. A further 6,426 await trial, although more than 3,000 of them live in exile.