Willie Kimani, his client and driver were abducted, tortured, killed and their bodies dumped in a river.
A Kenyan court has found three policemen and a civilian guilty of the murder of a human rights lawyer and two other people in June 2016.
The bodies of Willie Kimani, his client and a taxi driver were found after they had been dumped in a river on the outskirts of the capital, Nairobi.
The case caused national outrage and highlighted the many extrajudicial killings and disappearances that have been blamed on the Kenyan police.
A fourth policeman was acquitted.
“I am satisfied that there was no other reasonable hypothesis that can be made on the basis of the evidence before me except that of guilt,” Judge Jessie Lessit ruled.
Kimani was defending motorbike taxi driver Josephat Mwenda who had accused policeman Fredrick Leliman – one of the three officers found guilty – of shooting him for no reason at a traffic stop in 2015.
Kimani, Mwenda and their taxi driver Joseph Muiruri were last seen on 23 June 2016 at a police station.
Their mutilated bodies were recovered two weeks later in a river almost 100km (62 miles) from the city.
Outside court, Kimani’s widow Hanna said the verdict had brought justice and was “a source of comfort to our hearts, even though it may not bring Kimani back”.
“At least Kimani will not be included in the statistics of people who went through torture, went to abduction, tortured and killed without getting justice,” she said.
Benson Shamala, the Kenya director of International Justice Mission, where Kimani worked said: “No-one should go through what our friends… went through and especially from the very people mandated to protect them.”
Kenya’s Independent Policing Oversight Authority (IPOA) has recorded more than 6,000 complaints, according to data the agency has gathered since its creation 10 years ago, but few officers have been prosecuted.
Mr Shamala said that Friday’s judgement showed that Kenya’s justice system was capable of “delivering justice in cases of police abuse of power”.
“This landmark decision will send a strong message to rogue police officers who abuse their powers that they will be held accountable under the law,” he said in a statement.
IJM commended the prosecutors adding that since the 2016 killings, more than 40 police officers had been convicted of murder or manslaughter.
Sentencing for the three officers and the civilian, who was as a police informant, will be announced at a later date.