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NAIROBI (Reuters) - A court in Kenya convicted an ex-senior police officer of murder on Thursday in the death of a suspect taken into custody in 2013, in what rights groups welcomed as a further step toward curbing years of police brutality.

Activists long accused police in the East African country of using excessive force with little risk of being charged or convicted. A police oversight authority set up in 2011 ended virtual police impunity and fostered prosecutions for abuses.

Former senior police officer Nahashon Mutua was found guilty of the murder of Martin Koome, who was found dead in a cell at a Nairobi police station where Mutua was in charge.

“I find the prosecution has proved its case beyond reasonable doubt and I believe the deceased died of injuries he sustained while in police cells,” said High Court Judge Stella Mutuku, remanding Mutua in custody until sentencing next week.

“The former senior policeman misused his powers of authority and flouted the law so as to cover up the case,” Mutuku said, dismissing the argument of Mutua’s defense that Koome was fatally beaten by other inmates.

Kenya’s Independent Police Oversight Authority watchdog led the investigation that brought charges against Mutua. “This is a wake-up call to other police officers to perform their duties within the law..., IPOA spokesman Dennis Oketch said.

“The judgment is a big step towards holding errant police officers to account,” anti-violence organization International Justice Mission said in a statement.

IPOA, established seven years ago after police killed hundreds of Kenyans during unrest that followed disputed elections in 2007, can investigate police on its own initiative or after receiving a complaint from the public.

It has the power to order any serving or retired officer to appear before it. IPOA submits the findings of its investigations to prosecutors, who decide whether to pursue a criminal trial or order an inquest.