The body of a Kenyan lawyer who was representing a client making a complaint against the police has been found.
The Law Society of Kenya (LSK) said Willie Kimani's death was a "dark day for the rule of law in Kenya".
Kenya's police have often been accused of brutality and they have been blamed for a series of extrajudicial killings.
The police chief has ordered the arrest of three police officers suspected of being involved in his kidnapping.
Mr Kimani, who was 32, went missing along with his taxi driver and client after a court appointment over a week ago, the LSK said.
One other body has been found but there are conflicting reports as to who this is.
Kenyans and their police: By Nancy Kacingura, BBC News, Nairobi
The relationship between Kenyans and their police force has always been an uneasy one.
Just a week ago, the National Police Service spokesperson came out to ask Kenyans to change their perception of the police.
He said he had noted that "there is pervading fear among the public as they believe that law enforcers are working with criminals".
He's not wrong. Many victims of crime would rather forsake justice than go through the process of dealing with the police. It is largely seen as a fruitless and frustrating endeavour.
The police service has worked to improve its image over the past 10 years - changing its name, vetting its officers, instituting community policing and establishing gender and children desks.
But it appears that the more recent incidents of police beating protesters at a demonstration, and a wave of controversial killings, are still sending the Kenyan public a much louder message.
A police source told the BBC that the two bodies had been found on the bank of a river 70km (43 miles) north-east of Nairobi.
Mr Kimani's body was found bound and wrapped in a sack, reports AFP news agency.
A search is ongoing at the site to find the third body, Kenya's Standard newspaper reports.
On Thursday, the inspector general of the national police service George Kinoti said that investigations would be pursued.
"In the event that a crime is disclosed linking any person, whether police officer or otherwise, the law will doubtless take its own course," he said in a statement.
Mr Kimani was working for the International Justice Mission, a US legal charity which focuses on cases of police abuse of power.
He had been representing his client in a complaint against a police officer who had allegedly shot him during a traffic stop in 2015.
LSK says this is the first time that a lawyer working on a sensitive case has gone missing.
However, LSK head Isaac Okero told the BBC's Mohammud Ali in Nairobi that the incident suggests "lawyers are becoming a target because of their work".
In 2011 a Kenyan human rights lawyer accused the Kenyan government of framing him for a bombing to get back at him for defending victims of extraordinary rendition.
Kenyan security forces carried out 25 extrajudicial killing between 2013 and 2015, Kenya's official rights body said.
High-profile extrajudicial killings in Kenya:
- In May 2016 Businessman Jacob Juma was shot dead while driving home. He had been involved in several high-profile legal cases against the government over failed business deals
- In October 2013 Muslim cleric Ibrahim "Rogo" Omar was shot dead while driving home. Mr Rogo was alleged to have links with Islamist militants al-Shabab
- In August 2012 Muslim cleric Aboud Rogo Mohammed was killed in a drive-by shooting. He was from the same mosque as Mr Omar and was also accused of backing al-Shabab
- In March 2009 human rights activist Oscar Kamau Kingara, who investigated extrajudicial killings, was shot dead in his car shot as he drove home.