What could possibly link an ultra-luxury spa hotel on the Aegean Sea in Greece, the most violent criminal gang in Russia’s living memory, and a web of prosecutors in the country, leading right up to the family of the general prosecutor?

According to the latest investigation by Russia’s anti-corruption campaigner, Alexei Navalny, and his team, the sons of the country’s general prosecutor, Yuri Chaika, have amassed a huge business empire, thanks at least in part to their father’s position and their ability to keep regional prosecutors onside.

It also alleges that the sons’ business associates have ties to the Tsapok gang, which terrorised the town of Kushchevskaya in southern Russia until arrests were made following a massacre that shocked the country.

Navalny’s 45-minute video begins with a five-star hotel in Halkidiki, Greece. The hotel’s lavish opening featured a speech by Russia’s culture minister, Vladimir Medinsky, and performances by leading Russian pop stars.

Navalny’s researchers discovered that the owners of the hotel were Artem Chaika and Olga Lopatina, the former wife of Gennady Lopatin, the deputy prosecutor general and Yuri Chaika’s number two.

Navalny has made a habit of uncovering the undeclared property, suspicious foreign assets and criminal links of Russian elites, usually to a stony wall of silence as an official reaction, but the Chaika video is the most damning yet, if the allegations are all true. Chaika’s other son, Igor, is also accused of using his family connections to build a huge business, and of benefiting from apparently rigged state auctions.

Navalny said his team first uncovered the Chaika story when they were doing their regular monitoring of property purchases in territories where Russian officials like to stash their money – Greece, Cyprus, Spain and London. They noticed the lavish Greek hotel opening and the Chaika connection.

“We put it to one side for a while, because really there’s nothing all that surprising in our officials having dubious property. But then, when the Tsapok links appeared, I couldn’t believe it initially.

“We checked it and checked it, and it just got worse and worse,” he told the Observer.

Navalny’s anti-corruption foundation found company records showing Lopatina was one of the joint owners of a sugar business with Anzhela Tsapok, the wife of Sergei Tsapok, who died in prison last year. He had been given a life sentence for one of the worst crimes in recent Russian history.

Even in Russia, in which the crime pages of newspapers are often filled with gruesome deeds, the Kushchevskaya massacre resonated for its sheer brutality. Twelve people were killed, including four children, mainly by stabbing or strangulation, and then the house was set on fire with the bodies inside. The ensuing investigation uncovered a chain of killings, kidnappings, rape and corruption. Tsapok, who had formerly been a local politician, was named the gang leader and sentenced to life in prison, while his mother was given three years in prison for fraud.

The prosecutors in the case at the time said Tsapok’s gang had its tentacles all over the town, with local police on the payroll. Tsapok himself was a member of the pro-Kremlin United Russia party and a member of the local parliament.

The gang controlled all local business, and were also accused of picking young women at random off the street, raping them and then keeping them silent with threats. They were accused of 19 deaths over a decade, including the 12 which brought Moscow police to the town and finally uncovered the chain of wrongdoings that local police had been unable or unwilling to prosecute.

Navalny’s film includes documents which appear to show that earlier cases against the Tsapok gang were dropped after interference from local prosecutors. Navalny’s video has received more than 3 million views on YouTube in the week since it was launched, but the official reaction has been muted.

Vladimir Putin’s spokesman, Dmitry Peskov, said the allegations “did not provoke our interest” because they were not related to the general prosecutor but to his sons, who have their own business activities.

Chaika himself, in his only comments on the video, told Interfax on 3 December that the video was “a hatchet job, not paid for by those who made it”, hinting that some outside power was attempting to smear him. “The information presented is deliberately falsified and has no basis in fact,” he said.

Prime minister Dmitry Medvedev was asked about the allegations during an annual interview with Russian journalists last week, and became angry, suggesting that tabling the accusations was risking a return to Stalin-era repression. “You said a certain person has been accused. If we’re going to operate in such a way, we’ll be going back a long way — back to the 1930s. Only law enforcement can lodge accusations,” he said.

The influential business daily Vedomosti wrote an editorial calling on the government to investigate the allegations seriously. “The materials that were published need to be confirmed, but they are not baseless – the investigation is well documented,” the paper wrote. “In a normal country, these kinds of public accusations should be publicly dealt with, and not just by the people involved but by their superiors.”

Navalny said the authorities were in a difficult position, as they did not want to be seen to be reacting to any of his investigations. He is also an opposition politician and a trenchant Kremlin critic. He has faced a number of court cases and his brother has been jailed, in what has been described as an attempt to put pressure on him.

“There will not be any investigation here, but the Latvian authorities have already started one on money laundering and we want the Swiss authorities to start one too. We want to make the cost of keeping Chaika very high for the Kremlin,” Navalny said.