Tens of thousands of Cambodians have marched in the funeral procession for a leading government critic who was fatally shot in an attack that raised suspicion of a political conspiracy.

Kem Ley was shot on July 10, and a former government soldier told police he killed him over a money dispute. The suspect's wife, however, said they were too poor to loan money.

The massive procession on a 70-kilometer (50-mile) journey started at dawn Sunday from a Buddhist temple in Phnom Penh to Kem Ley's hometown in Takeo province.

Prime Minister Hun Sen, often a target of Kem Ley's criticism, has promised a thorough investigation into the killing, which came at a time of political tensions that began last year with legal and other pressures against the opposition.