For the 2016 killing of human rights advocate Willie Kimani, the court has sentenced three policemen and their civilian accomplice to decades in prison.
Shortly after submitting a complaint of police brutality saying that Mwendwa had been shot and wounded by police, Kimani, his client Josephat Mwendwa, and their driver Joseph Muiruri were all killed.
Later, their bodies were found in a river near Nairobi.
In Kenya, where police are frequently accused of brutality and extrajudicial killings but hardly ever convicted, the case caused uproar.
Last year, the four suspects were found guilty of murder.
The court gave Frederick Leliman, the main defendant, a death sentence. Kenya has not carried out an execution since 1987; instead, death sentences are frequently modified to life in prison.
The punishments for the other two police officers, Stephen Cheburet and Sylvia Wanjiku, as well as their informant, Peter Ngugi, ranged from 20 to 30 years in prison.
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