Hundreds of people marched through Kenya's capital on Monday condemning "extrajudicial executions" following the murder of three men, including a lawyer who criticised police abuse.
Dressed in T-shirts smeared in red paint to symbolise blood, the demonstration organised by the Kenya National Commission on Human Rights called for investigations into the killings. Three police officers are in custody.
The bodies of lawyer, Willie Kimani, his client Josephat Mwenda and driver Joseph Muiruri, who disappeared on June 23, were found on Friday by a riverbank outside Nairobi.
When the authorities found his body, Kimani's wrists were bound with rope, three of his fingers had been chopped off and his eyes appeared to have been gouged out.
A joint statement by 34 Kenyan and international human rights organisations condemned the killings.
"These extrajudicial killings are a chilling reminder that the hard-won right to seek justice for human rights violations is under renewed attack," said Muthoni Wanyeki from Amnesty International.
Law Society of Kenya chairman Isaac Okero rejected police claims of an "isolated case involving a few rogue officers" and demanded the government take action.
"Many, many Kenyans have gone missing, and this is a situation that is completely intolerable," Okero said.
Kenya's police force has been accused in the past of running hit squads targetting those, including human rights activists and lawyers, investigating allegations of police rights abuses.
"Cases of police killings are emerging from many parts of the country each year," said Otsieno Namwaya, from Human Rights Watch.
"The government should urgently conduct a thorough investigation to ensure that perpetrators are held accountable and that these killings stop."