This week a jury acquitted PC Harwood of the manslaughter of Ian Tomlinson at the 2009 G20 protests. It was widely reported – for example, in the Evening Standard and Guardian – that the juries in both the manslaughter trial and the original inquest did not hear about previous, mostly unproven, allegations of misconduct and use of excessive force on the part of Harwood. Many people are now asking why the jury did not hear this evidence.

Historically, if a defendant had previous convictions, or there was evidence of previous allegations, the legal starting point would be that such evidence should not be used against them. The reason behind this is clear: if a jury hears that a man accused of burglary has several previous convictions for burglary, there is always the risk that a jury would be far more likely to convict on the basis of his previous convictions, rather than the evidence in the actual case. The fact that someone has committed burglaries in the past doesn’t mean that he necessarily committed the one in question.

At the end of the day, it is important that criminal trials are not distracted by allegations that amount to nothing more than smears on a person’s reputation.

Since the changes in the law made by the Criminal Justice Act 2003 it has become much easier for prosecutors to use so-called ‘bad character’ evidence against a defendant. Under the current law, there are various legal tests which, if satisfied, mean that the evidence can be used at a trial. Ultimately, it is a matter for the judge to decide. In making that decision, there are two key factors that will be essential for the judge to consider.

Bad character
Firstly, the evidence has to be clearly relevant to an issue in the trial. If a person is accused of assaulting their partner, but has a previous conviction for shoplifting, that evidence is unlikely to assist a jury as to whether he has been violent. If, however, a defendant has a history of committing acts of violence, but claims to have acted in self-defence, whether or not he is violent and aggressive is something that the jury will need to consider.

If the character evidence will help the jury decide a relevant issue, the next thing to consider is whether the allegations or convictions are reliable and good evidence as to that issue. The judge will take into account the age of the convictions. The more recent the convictions are, the more likely they are to be admissible. It would clearly be unfair if someone has a conviction from 20 years ago for it to be brought up in court if it has no bearing on their character at the relevant time.

Equally, if there are factual similarities between previous convictions and the current allegations will be an important factor to any judge in deciding whether previous convictions can be used as evidence. If a burglar has a typical way of working, for example he always commits burglaries at night, using a lock pick, in the same geographical area, then that will assist a jury if the facts are similar to the current allegation. On the other hand, if a defendant had previously committed a single opportunistic burglary of a house that he had noticed was unoccupied, this would be quite different to a professionally planned burglary of commercial premises.

Where the evidence is that of previous unproven allegations, as reported in the Harwood trial, the decision for the judge is particularly difficult. The fact that allegations are unproven does not necessarily mean that they cannot be used as evidence. For example, in cases concerning domestic violence, where there is often a pattern of allegations being made to the police before a conviction can be secured. Equally, if an unproven allegation is put before a jury, then it is only fair for the defendant to be able to explain it to them. That might involve calling his own evidence to rebut the allegation. The obvious risk is that the jury are distracted from the central issues of a case by having to make decisions about whether allegations are correct. This can make things particularly difficult for a defendant, particularly if the allegations concern conduct some time in the past, and it might be difficult to prove whether they are untrue or not.

Rather than risk a jury just assuming someone is guilty because of past conduct, it is sometimes the case that the only way in which someone can have a fair trial is to not allow such allegations to be used against them. That is what was decided in PC Harwood’s case. Ultimately, no matter what the outcome of any particularly trial is, it is right that fairness to is at the heart of criminal proceedings, and that convictions are firmly based on the evidence that has been demonstrated to be both reliable and relevant.