An influential human rights activist and his colleague have been shot dead in central Nairobi in an organised killing that sparked accusations that they were assassinated by security forces.

A week after a UN expert described the Kenyan police as “a law unto themselves” the cold-blooded shooting of Oscar Kamau Kingara and John Paul Oulu threatened to send strained relations between the olice and its population to a new low.

Mr Kingara and Mr Oulu were ambushed as they sat in a white Mercedes in rush-hour traffic on a road outside the University of Nairobi’s halls of residence. Three gunmen in dark suits fired repeatedly into the car. Mr Kingara was killed outright and Mr Oulu mortally wounded. Witnesses said the killers sped away in two cars.

Hours before the attack a government spokesman had berated Mr Kingara publically for allegedly helping the outlawed Mungiki criminal sect. Mr Kingara’s death immediately raised suspicions that the police and State were responsible.

“The human rights community in Kenya holds the Government fully and wholly responsible for the assassinations,” said Cyprian Nyamwamu, of the Kenya Human Rights Consortium. The police deny any government responsibility for the murders. The Prime Minister, Raila Odinga, condemned the killings and warned that the country was at crisis point. “We are hurtling towards failure as a state,” he said.

After the attack students fearing that police would remove important evidence and with it the best chance of finding Mr Kingara’s attackers, pushed the shot-up Mercedes into their halls of residence compound and hid Mr Kingara’s body in a stairwell.

“Without the body there is no evidence,” said one angry student, a 22-year-old who did not want to be named for fear of police reprisals.

A stand-off ensued between dozens of students holding the corpse and police reinforcements that arrived in trucks after dark. The police used tear-gas and live ammunition, while the students threw rocks and chunks of masonry.

After more than three hours, the police found Mr Kingara’s body and drove away with it, but not before one of the students was shot dead by an officer. Three policemen have been arrested for that killing.

Yesterday the dead student’s blood was still fresh on the ground near the gates, surrounded by pebbles and protected by grieving classmates who refused to allow it to be washed away.

Mr Kingara’s Mercedes remained jammed against a wall outside the student bar, a thick trail of smeared blood leading past the pool table and into the dingy stairwell where his body had lain.

“It is clear the police are utterly compromised,” said Ben Rawlence, Kenya researcher at Human Rights Watch.

Mr Kingara, the founder of the respected Oscar Foundation Free Legal Aid Clinic, published a report last year accusing the police of torturing or killing more than 8,000 Kenyans in a crackdown on the Mungiki.

Earlier on Thursday the Mungiki – a Kikuyu tribal gang that runs protection rackets and is responsible for many gruesome murders – held its own protests against police violence.

“It is imperative, if the Kenyan police are to be exonerated, for an independent team to be called from somewhere like Scotland Yard,” said Professor Philip Alston, the UN special rapporteur on extrajudicial killings. Last week Mr Alston issued a damning indictment of Kenya’s police and its British-trained army. At the end of a ten-day fact-finding mission he concluded that Kenya’s police “kill often, with impunity”.

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