Nobel laureate Malala Yousafzai has visited the office of the International Justice Mission in Kenya's capital and offered condolences for the human rights lawyer and two other men whose killings have caused an uproar.

Lawyer Willie Kimani, client Josephat Mwenda and taxi driver Joseph Muiruri are suspected to be victims of police-linked extrajudicial executions. Lawyers and others protested across Kenya after their bodies were pulled out of a river July 1.

Autopsy results show they were tortured. Four police officers face murder charges over their deaths.

Kimani was representing Mwenda in pursuing charges against a police officer for shooting him in an unprovoked incident in April 2015.

Rights groups say extrajudicial killings by police are common in Kenya. Independent Medico Legal Unit says there have been 520 since 2013.