Kazakhstan's KNB security service has said five of its officers have been arrested over the murder of opposition politician Altynbek Sarsenbaiuly.
Altynbek Sarsenbaiuly became a critic of the Kazakh government
The KNB said the five were members of its elite Arystan combat division.
Opposition groups have accused the government of involvement in the death of Mr Sarsenbaiuly, who was found shot dead by a roadside earlier this month.
He was the second opposition politician to be found dead in mysterious circumstances in recent months.
The KNB in a statement called the arrested men "werewolves in epaulettes", a term for corrupt security officials, according to the Reuters news agency.
A sixth man, who was also arrested for organising the operation, was a former law enforcement officer, opposition leader Zharmakhan Tuyakbai told the Associated Press.
The five men accused of committing the murder were paid $25,000, according to Interior Minister Baurzhan Mukhamedzhanov.
Mr Sarsenbaiuly, a former minister and ambassador, was President Nursultan Nazarbayev's close ally until 2003, when he defected to the opposition.
His body was found outside the commercial capital, Almaty, with bullet wounds in his back and neck. His bodyguard and driver had also been killed.
The killing was condemned by opposition groups, who accused the government of President Nazabayev of seeking to silence any critics.
In November, in the run-up to a presidential election which saw Mr Nazabayev easily retain power, another opposition figure - Zamanbek Nurkadilov - was found dead at his family home in Almaty with a revolver by his side.
An official enquiry concluded that it was a case of suicide.
But a lawyer for Mr Nurkadilov's family questioned whether it would have been possible for the former mayor of Almaty to shoot himself twice in the chest before delivering a final shot to his head.