Tens of thousands of Cambodians turned out for a funeral march last month including his heavily pregnant wife Bou Rachana and their four children.

They have since left Cambodia, fearing for their safety, friends said.

“[Kem Ley’s wife] and her sons are now at a safe place, they are not in Cambodia,” Tim Malay, head of the Cambodia Youth Network and one of the funeral organisers said.

But Buntenh, head of the Independent Monk Network for Social Justice, confirmed their departure.

“His family left the country for a safe place on August 28,” he said. “They are now staying at a safe place abroad.”

Both declined to say where the family had fled to.

A former soldier has been charged with the murder, claiming he shot Kem Ley over an outstanding debt.

But suspicions of a political assassination continue to run strong in a nation where the rule of law is threadbare and critics of the elite are routinely silenced.

A regular critic of both Hun Sen and the political opposition, Kem Ley had called for a new era of clean politics in graft-ridden Cambodia.

The frequent radio commentator was also a major advocate for land and labour rights, travelling across the impoverished country to speak directly to villagers.

Last month’s funeral march was one of the largest public gatherings in recent years in Cambodia, highlighting how the murder had touched a nerve.

Shortly before his death Kem Ley gave a lengthy radio interview welcoming a report that detailed the riches amassed by Hun Sen and his family during his three decades in power.

Hun Sen has ordered a thorough investigation into the murder and urged people not to turn the case into a “political act”.