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.

A farm worker told police he killed Kem Ley, 45, over a $3,000 loan. However, the suspect’s wife said the family was too poor to lend so much money. Cambodia has a brutal history of political violence.

Although there was no overt political sloganeering during the procession, the huge crowds reflected the massive anti-government sentiment that could pose a challenge to the prime minister Hun Sen, who was a frequent target of Kem Ley’s criticism.

Since the murder on 10 July, Kem Ley’s body had been kept at a Buddhist temple in Phnom Penh, Cambodia’s capital, for people to pay respects. It was placed in a glass casket on a decorated vehicle that set out at dawn and took almost 12 hours to complete the 43-mile (70-kilometre) journey to his hometown in Takeo province for the funeral on Monday.

A float carrying Kem Ley’s widow, Bou Rachana, and children, dressed in the Buddhist mourning colour of white, drove ahead of the hearse, which was followed by people, some carrying his portraits, on foot, motorcycles, cars and motor rickshaws.

Most of the marchers wore white T-shirts with pictures of Kem Ley, and some had printed slogans, including “Wipe your tears and continue your journey.” Many also waved religious and Cambodian flags in what appeared to be one of the country’s biggest public rallies in recent times.

Crowd numbers were hard to estimate, because the procession was constantly moving and many were in cars and other vehicles. However, with people gathered all along the route, and large numbers also at the destination, claims of 100,000 or 200,000 appeared credible.

The last such turnout was when opposition leader Sam Rainsy returned from exile in July 2013. Sam Rainsy, the strongest rival to Hun Sen, survived a 1997 grenade attack on a rally of his followers that killed 16 people and wounded more than 100. No one was ever brought to justice.

Kem Ley is the most prominent Cambodian government critic to be killed since trade union leader Chea Vichea in 2004.

Many in Sunday’s crowd spoke of their admiration for Kem Ley, who was known mainly for his commentaries on radio broadcasts from overseas outlets such as Voice of America. Most mass media in Cambodia is under the control of the government and its supporters.

“I regarded him as my god because of his bravery, cleverness. His death was as if I had lost something personal,” said Chhun Eang, holding Kem Ley’s portrait. Visibly upset, she said she travelled from north-western Battambang province, 186 miles (300km) away, to attend the procession. “Why are good people like him always killed?” she said.

Long Kiet, a 70-year-old retiree, said Kem Ley was killed because he criticised the government. “They are not scared to kill anyone who dares to criticise them. It doesn’t matter if he or she speaks right or not,” Kem Ley said.

Several lawmakers from Sam Rainsy’s Cambodia National Rescue party also joined the procession, and Sam Rainsy’s Facebook page carried the event live.

As the convoy passed, onlookers bowed their heads with both hands placed together out of respect. Several hundred police, including units in riot gear, were deployed along the route, particularly visible in front of Hun Sen’s office, where anti-riot trucks and teargas guns were on standby.

Hun Sen has condemned the attack and promised a thorough investigation into the killing, which came at a time of political tension that began last year with legal and other pressures by the government on the Cambodia National Rescue party. Sam Rainsy is abroad to avoid being jailed on legal charges many consider politically motivated.