Any criminal justice system worthy of the name will throw up lots of anomalies, but in the case of the death of Ian Tomlinson, the newspaper seller who died during the G20 protests in London in 2009 shortly after being struck and knocked to the ground by a police officer, Simon Harwood, the British system has apparently excelled itself.

First of all, there’s the fact that the assault on him would never have come to light if things had been left to the Metropolitan Police, which in recent years has sometimes functioned as a part-time subsidiary of News International. It was only reporting by the Guardian‘s Paul Lewis, and an American businessman’s cameraphone video of the assault, that launched the independent inquiry which eventually led to the trial of Harwood for manslaughter.

The Met’s performance in the case was truly lamentable. Tomlinson’s family were discouraged from speaking to journalists and initially prevented from seeing his body. They were not told of the three police officers who, 48 hours after Tomlinson’s death, said they had seen a colleague strike him with a baton and push him to the ground. And for five days the family were denied details of the bruises and dog bites on the dead man’s legs, not to mention the three litres of bloody fluid found in his stomach.

Then there was the conflict in pathologists’ opinions on the probable cause of Tomlinson’s death. The first pathologist opined that he had died from a heart attack. QED. But after the Guardian published the camera phone video, the Independent [sic] Police Complaints Commission (IPCC) launched a criminal inquiry and further post-mortems concluded that Tomlinson had died from internal bleeding caused by blunt force trauma to the abdomen, in association with cirrhosis of the liver. In May 2011, a inquest jury returned a verdict of unlawful killing, which then led to the prosecution of PC Harwood for manslaughter. Yesterday, he was found not guilty on a majority verdict of the jury.

So now we have two contradictory verdicts: unlawful killing; and acquittal of the only person who might have been implicated in the death.

Fair enough, you may say — though obviously very hard on the Tomlinson family. Our justice system stipulates that juries have to be convinced “beyond reasonable doubt” and members of this panel clearly were unable to convince themselves that there was an unambiguous causal connection between Harwood’s assault and Tomlinson’s death.

But then came the revelations of the information about Harwood that had been withheld from the jury. It turns out that he has had a chequered history as a police officer, including disciplinary hearings over allegations of having punched, throttled, kneed or threatened suspects while in uniform (although it should be said that only one of these complaints was upheld).

Question: would the criminal trial jury’s verdict have been different if they had known about Harwood’s background?

Answer: possibly yes, which is why so many lay people today are outraged by the acquittal. But keeping the jury in the dark was the right thing to do, given the values embodied by our justice system. Harwood was not being tried for his past, but for this particular offence. People are innocent until proven guilty, and even bad eggs can be innocent of a particular crime, no matter how heinous their backgrounds might be.

It’s an interesting case of the importance of intangible values. A justice system which convicted people on the sworn testimony of a police or Intelligence officer would doubtless be a highly efficient one. But we — rightly — value justice more highly than efficiency. And, as m’learned friends sometimes say, hard cases make bad law.