Oeuth Ang, who calls himself "Meet to Kill," admitted at his trial that he had killed staunch government critic Kem Ley at a cafe in the capital Phnom Penh last year.
A Cambodian court on Thursday sentenced Oueth Ang to life in prison for killing prominent activist and government critic Kem Ley last year.
Ley, who was a staunch critic of the government, was shot at a cafe in the capital Phnom Penh on July 10, 2016.
His murder sparked protests and saw tens of thousands of people take to the streets against a backdrop of growing political tensions with veteran Prime Minister Hun Sen, who was gearing up for elections at the time.
Oeuth Ang, an unemployed ex-soldier who calls himself "Chuob Samlab" or "Meet to Kill," admitted the killing, saying it was over a $3,000 debt.
In his sentence, Judge Leang Samnath said Ang had been given life imprisonment for premeditated murder and possession of a gun without permission.
TRT World spoke to South Asian specialist and journalist Luke Hunt about the sentence.
Possible political assassination
Rights groups have remained doubtful over the apparent motive as assassinations of activists and government opponents are common in the country.
They said the killing of Ley was politically motivated because of his caustic commentaries about Sen and his government.
Kingsley Abbott, a senior international legal advisor at the International Commission of Jurists, called for the investigation to be reopened.
"Until there is an independent, impartial and effective investigation to establish whether anyone else was involved in the killing, the victims of this terrible crime, including Ley's wife and children, will be unable to obtain justice."