Suppose that, in a future season of Line of Duty, the reveal turned out to be that the organised crime syndicate had been using hitmen to kill drug dealers in a conspiracy with a Crimewatch presenter to raise ratings for the show. Social media would surely be filled with shark-jumping memes. Yet it is possible that such an absurd sequence of events happened for real in Brazil. This strange tale is the subject of Killer Ratings, an astonishing documentary series that has just dropped on Netflix.

At a time of moral panic over television ethics in Britain, an even more extreme example can be found in the story of Wallace Souza, host of Canal Livre (English translation “Free Channel”) , which became the most-watched news show ever in Amazonas, a state in north-west Brazil.

Souza’s shtick as a TV presenter was “defender of the public”. There is a recognisable pious relish in a clip where he confronts a criminal, live on camera, with the accusation: “You murdered a citizen in front of a child.” Another highlight of Souza’s showreel was a sequence in which holed-up gangsters agree to negotiate in person only with the TV star. They took him hostage, but the public’s defender talked himself free just in time to come live to the studio to report on his ordeal.

Watch the trailer for the Netflix documentary series Killer Ratings

Because guidelines on editorial impartiality seem to be less strict for broadcasters in Brazil than the UK (where Martin Bell had to leave the BBC to be an MP) or the US (where Donald Trump gave up The Apprentice to be president), Souza was able to both present his show and be elected three times, with ever more crushing majorities, as a member of the state assembly. From that platform, he criticised cops and judges for their failure to impose justice as fiercely as he did on TV, where Canal Livre became ever more lucrative for its channel, TV Rio Negro, by featuring “exclusive” solutions to drug-war executions that the police had not yet got round to investigating.

Imagine a Brazilian combination of David Attenborough, Sherlock Holmes and Barack Obama, and Souza seemed, by 2009, to have become it. However, following a plea-bargaining confession by a crook arrested in a separate case, it was alleged that Canal Livre was arriving so quickly to the sites and perpetrators of crimes it was covering because it had arranged for them to be committed. Although compelling evidence was found at the presenter-politician’s home, he insisted that he was being framed by ministers and police chiefs infuriated by his programme’s exposure of their failings.

Without plot-spoiling, audiences should be warned that real stories cannot always be resolved as neatly as fiction; a sudden occurrence (easily found by Googling, though those who are spoiler-averse may want to steer clear) prevents complete closure in this case. However, the effect of this uncertainty is to make viewers into jurors, as is anyway often the case with true-life crime.

Although British and US TV have seen no ethical breaches remotely as severe as those of which Souza was accused, Netflix’s seven-part series does serve as an admonitory parable for all broadcasting organisations.

Wallace Souza, seen here hosting Canal Livre. Photograph: Antônio Menezes Antônio Menezes/PR Company Handout

Finding journalistic fault with the government, the police, the welfare system, and the judiciary, Souza seems progressively to have assumed their functions, becoming a combination of populist demagogue and vigilante enforcer. While one consequence of the allegedly commissioned killings and their swift solutions was to raise the profile of his show, another was to reduce the numbers of criminals on the streets, which might have been given as warped justification for the murders.

Without ever yet going so far, the British media have sometimes become impatient with the slow processes of justice, most notoriously in 2010 when they more or less convicted a Bristol teacher, Christopher Jeffries, of a murder of which he was completely innocent. And whatever the causal relationship between The Jeremy Kyle Show and the death of a guest may turn out to be, Kyle, and other such formats, are clearly vulnerable to the charge of turning a studio into a police cell or court. We can also all name political presenters who give the impression that they know better how to run the country than the people who are doing so.

Some argue that British TV is over-regulated, but Killer Ratings, a jaw-dropping story compellingly told, may make us thankful that barriers are in place to prevent broadcasters with delusions of becoming politician, cop, judge or jury from doing so.

• Killer Ratings is on Netflix now