On Saturday afternoon, Oleg Mihalik was among hundreds of protestors who tore down the fencing around what they say is an illegal construction project despoiling the seafront in Odessa, southern Ukraine. Seven hours later he was lying in a pool of blood after being gunned down.

Mr Mihalik was shot as he was returning to his home in the city centre, just over 100m from the headquarters of Odessa Regional Police.

He managed to stagger to the front door where a neighbour found him and called an ambulance. Doctors found at the hospital that the bullet had gone through his arm into his chest, just missing his heart.

On Sunday afternoon, as preparations were being made for surgery on the 43-year-old, his relations, friends and fellow activists gathered outside the police headquarters, demanding to know what was happening with the investigation and angrily pointing out that this was the latest brutal attack on those protesting against corruption in the city.

A senior officer at the station insisted that all efforts will be made to catch those responsible. No motive has been established yet for the attempted murder.

Mr Mihalik’s wife, the mother of his two children, was with him in hospital while friends outside the police station were trying to find out whether he was out of danger.

“His condition was very serious, but it might be stabilising,” said one of these friends, Mikhail Golubev, “which is good news.”

He counts the numbers of activists he personally knows who have been assaulted in the past two years: the number comes to six. No one has yet faced justice in any of these cases.

“Oleg was a peaceful guy who was very concerned by the abuse of the environment, how our natural heritage is being sold off illegally, about things like poaching,” Mr Golubev said .

“He was not some young radical – he never got involved in fights. We have now come to accept that we will be targets”.

Mr Golubev, a former professional chess player, continues: “I can, I suppose, be wounded or killed, the possibility is there.

“This makes it very difficult for my family. We have very powerful, very dangerous men with power and influence in this place, but we cannot just stop the work we are doing.”

Odessa has become particularly notorious, even by Ukraine’s low standards, for grand-scale larceny of public land as well as public money by a powerful and entrenched alliance of organised crime, politicians and oligarchs.

Successive governments in Kiev have declared they recognise the problems in the port city and have tried to rectify the situation.

We have very powerful, very dangerous men with power and influence in this place, but we cannot just stop the work we are doing

But they have failed. In one of the most highly publicised examples, President Petro Poroshenko appointed the former Georgian president, Mikheil Saakashvili, as governor of Odessa with a brief to clean the place up.

The two men subsequently had a bitter falling-out, with Mr Poroshenko first sacking Mr Saakashvili, then stripping him of his newly bestowed Ukrainian citizenship and then attempting to arrest and deport him.

In the days before armed police seized him in December last year, Mr Saakashvili told me at his office in Kiev: “I was sabotaged in Odessa. At first the local mafia feared me, but then they began talking to their corrupt friends here in the capital and realised they had nothing to fear because all my efforts would be undermined.”

The effectiveness of Mr Saakashvili’s tenure as governor is a matter of debate.

But Mr Mihalik and his fellow demonstrators, whom I meet at their protest at Langeron Beach on Saturday, say they know only too well that the corrupt elite have little to fear in carrying out massive fraud with impunity and retaliating against those who try to stand up to them.

Among those present is Svetlana Pidpala, an environmentalist and activist. She has campaigned against public and green spaces being illegally sold off to be turned into apartment blocks and shopping malls, and has become a target of the vested interests.

Last year she was viciously assaulted outside her home by two men on a motorcycle who punched and kicked her to the ground.

“They came from behind and after that all I can remember is being repeatedly hit and the pain that came with it,” she recalled.

“Luckily, there were people who came running to help, otherwise it could have been worse.”

The people who ordered the attack on her have not been caught, and she has little hope that they will be.

“You learn some facts of life here, and one of them is that these people will get away with it,” she said.

Vitaly Ustimenko is also present at the demonstration. The journalist and activist is part of an organisation seeking to expose corruption. It is in talks with the groups that will choose judges for anti-corruption courts being set up in Ukraine at the insistence of the US, European Union and the International Monetary Fund, which is keeping the country’s ailing economy afloat.

One of the projects he and a colleague, Oleg Pashak, are involved in focuses on examining the unexplained wealth of country’s judges and prosecutors.

Three months ago Mr Ustimenko, 25, was stabbed in the head, shoulders and legs outside the television station where he works.

“I was told the weapon used was one of those hand-made ones you find in prison,” he said. “The police came quite quickly – in fact, the chief of police came in person.

“They say they are carrying out an investigation, our lawyers are monitoring the investigation and we are providing documents. They haven’t caught anyone, and at the moment I get police protection.”

The police in Odessa have been accused of colluding with shady businessmen and the local mafia – allegations the force strongly denies.

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Hired thugs, the tityshki, are used to extort and intimidate with impunity, say activists.

The day before Saturday’s demonstration, a message appeared on social media saying: “I have work on 22 September after 9.30am. You must be taller than 180 cm, and weigh no less than 80 kg. We need muscle guys; this work will be more than just showing off for the cameras. Activists want to occupy the construction site, we need to stop them. The fee will be 1,000 hryvnias [£27], we can give you masks for your faces. If you want to join, send me a private message.”

There is no evidence that that the owners of the construction site were responsible for the posting.

There had been confrontations there during previous protests with private “security guards”. But that did not happen on this occasion – several hundred demonstrators turned up, many more than before, looking determined and, according to some of the police officers present, that may have been the reason the hired help kept away.

“It is not what happens in public that is the main worry,” Igor Bychkov, a fellow activist of Mihalik, said. “It’s when they find you on your own or just a few of you when it gets dangerous.