Kenyan lawyer Willie Kimani was tortured before being killed and his body dumped in a river, a pathologist has said in court.
Mr Kimani, his client and their driver were abducted last month after filing a complaint against the police. Their bodies were found a week later.
Four police officers have been arrested - they have not commented.
There have been nationwide protests, with complaints that extrajudicial killings are widespread.
Pathologist Andrew Gachie said Mr Kimani had 14 injuries to various parts of his body.
His skull and genitals had been crushed and he died from blunt force trauma to his head, the pathologist's report said.
Mr Kimani's client Josephat Mwendwa died from head, neck and chest injuries.
Their driver Joseph Muiruri had had a rope tied round his neck and died from strangulation.
Mr Mwendwa had filed a complaint saying he had been wrongfully shot by police.
The Law Society of Kenya is calling for the resignation of the police chief and the internal security minister.
On Monday, government spokesman Eric Kiraithe told the BBC's Newsday programme there were no "death squads" within the police force and that allegations of officers committing crimes would be fully investigated.
Kenya's official rights body says that Kenyan security forces carried out 25 extrajudicial killing between 2013 and 2015.
However, non-governmental watchdog Independent Medico-Legal Unit (IMLU) says the police killed 97 people in 2015 alone.
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 as he drove home.