Nothing could be more serious than the state taking the life of one of its subjects – except, perhaps, for the state's agents preventing this coming to light. After an inquest's ruling yesterday, it is now official that the newspaper vendor, Ian Tomlinson, was unlawfully killed amid the policing of the G20 protests in 2009. Many who saw the footage the Guardian obtained, which showed PC Simon Harwood striking Mr Tomlinson just before his death, will regard the verdict as a statement of the blindingly obvious. But it matters. For one thing it raises again the prospect of a prosecution; for another it invites searching questions about why it took so long to get the truth recognised.

The most immediate dilemma is for the director of public prosecutions. As he is required to do, he last night set the wheels in motion for reconsidering whether there is a realistic chance of a conviction. His unfortunate conclusion last year, which was not lightly arrived at, was that the mixed (and mixed-up) medical evidence precluded pinning responsibility beyond reasonable doubt on anyone. The inquest jury's considered view that the cause of death was "abdominal haemorrhage due to blunt force trauma", albeit it in a person whose susceptibility was increased by liver cirrhosis, surely moves things on. Justice in the individual case is still far from certain, but it is at least a possibility once again.

Even if it ultimately arrives, however, justice will have come via such a tortuous route that one has to wonder whether it could get lost next time. After a day on which many officers were concealing their identity badges, the Met dragged its heels. A botched postmortem followed, carried out by a physician who was under investigation. The Independent Police Complaints Commission said there was "nothing in the story" that Mr Tomlinson had died after a fatal run-in with the thin blue line, and it waited a full week before launching an investigation. Whether through incompetence, conspiracy or some mix of the two, every check that the citizen imagines him or herself to have against the authorities was initially frustrated.

Healthy democracies are distinguished from police states by the ideal that those who enforce the law should be subject to it in the same way as everyone else. For the most part this happens in Britain, but there can be chilling lapses in the most serious cases, as was seen in the pall thrown over Blair Peach's killing for 30 years, and in the failure to bring the Met to book over the de Menezes case, other than through health and safety laws. The killing of a newspaper salesman who was simply trying to get home raises all the old anxieties about state power which is accountable to none.