“I am not corrupt,” Thitisant said during a press conference last week, during which he claimed he had accidentally killed Jeerapong while trying to extract intelligence “to protect the Thai public” from the scourge of drugs.

He has since been stripped of his rank and taken into custody, with the police promising a fair and full probe into the incident.

But while Royal Thai Police Chief Suwat Jangyodsuk described it as the work of “one bad apple”, the case has enraged Thailand and energised whistle-blowers, who are doing their best to prove him wrong.

At least four videos have since been posted on Twitter purportedly showing police hitting, kicking, and beating people in custody, racking up hundreds of thousands of views.

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One video posted two days after Thitisant’s arrest, which has since been viewed more than 721,000 times, appears to show a man being struck by police while in hospital in August 2019, after several officers drew the curtains around his bed.

The death of suspected dealer Jeerapong has also seen a surge in allegations of abuse, overreach of power, nepotism, and bribery on Facebook pages popular in Thailand, such as the Free Thai Civil Servant group.

“Leaked evidence is very important if we want to see change and reform in the police force. Don’t let things go quiet,” one Bangkok police colonel told This Week in Asia on the condition of anonymity. “This scandal might shake the organisation significantly as Thai police are very concerned about their image … especially those aspiring for a big seat, they can’t have tainted history.”

Under the glare of public scrutiny, the Thai police have said they are pursuing murder, torture, and criminal negligence charges against Thitisant and his six subordinates.

“The prosecution of this case will be done according to the law,” Police General Suchart Teerasawat – the deputy chief of the national police, who is heading the investigation – told a parliamentary committee on Thursday. “There will be no support or exception for those who commit crimes.”

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But rights groups have warned that the kingdom’s police have a record of impunity.

“Successive Thai governments have a long history of failing to ensure accountability for even the most ghastly police abuses against people in custody,” said Brad Adams, the Asia director at Human Rights Watch.

According to Transparency International’s 2020 Global Corruption Barometer report for Asia, 37 per cent of citizens thought most or all members of the police were corrupt – the highest in the Association of Southeast Asian Nations (Asean) – while 47 per cent had paid bribes to the police in the past 12 months.

Prominent whistle-blower Chuwit Kamolvisit, a former massage-parlour tycoon who alleges he has paid millions of dollars in bribes to police so he can operate in the sex industry, said the issue stemmed from the embedded pay-to-play culture in the force.

“You want to open a pub or bar, you have to get permission from the cops, if you want to open a gambling ring you have to get their permission,” he said. “‘Grey businesses’ don’t exist just because police wages are low … it’s because of the amount of power they have been given so they can run an empire.”

The Thai police have not formally addressed the videos being posted on social media.

“How are we supposed to trust the police when they are worse than the villains?” key protest group the United Front of Thammasat and Demonstration said in a Facebook post on Friday. The group is leading a major anti-government rally on Friday evening in Bangkok.

“Thai police are all about connections and patronage,” the Bangkok police colonel said. “So in the long term you have to uproot the entire power structure if you want true reform.”