Political analyst and government critic Kem Lay was gunned down in July 2016, in a country with a history of assassinations.
The trial of a former Cambodian soldier who is accused of killing Kem Ley in July 2016 began in the capital Phnom Penh on Wednesday.
Ley was a staunch government critic. Many believe his murder may have been state-sponsored, and his death sparked widespread grief in a country with a dark history of political assassinations.
Oeuth Ang, 39, was arrested shortly after he allegedly shot Kem Ley on July 10, 2016 at a convenience store with his morning coffee and newspapers.
As the trial got underway, prosecutors read out the police report detailing Oeuth Ang's alleged motives.
"(It was) because he cheated me out of $3,000 and he promised to build a concrete house for me," the police report quoted Oeuth Ang as saying, adding that "nobody ordered me" to do the killing.
Tens of thousands turned out for Kem Ley's funeral last year in scenes that rattled the government of ruling strongman Hun Sen.
Sen's more than three-decade rule has seen multiple critics murdered in rarely solved cases, especially in the 1990s and early 2000s.
In the days before Kem Ley's death, the political analyst had given interviews on a bombshell report detailing the enormous wealth accumulated by members of Hun Sen's family.
The wives of Kem Ley and Oeuth Ang said the pair had never met.
Following Ley's murder, his wife, as well as friends of both the victim and alleged perpetrator, fled to Thailand. Ley's wife is seeking asylum in Australia.
Cambodian media reports also suggest the accused had rarely had a dollar to his name since leaving the army.
Information relating to the murder investigation has been withheld from the public. This includes security camera footage from inside the convenience store, stoking suspicion that the murder might have been politically motivated.