Plea in Mitigation
^ TOPMitigation
The defendant has either pleaded guilty (i.e. accepted that he did the thing alleged by the particular charge) or has been convicted after a trial. (Obviously if the defendant is found not guilty and acquitted then there is no question of being sentenced and the defendant is free to go). The prosecution have outlined the facts and any previous convictions, and provided the victim impact statement if there is one. Before the Judge passes sentence, the defence have the opportunity to mitigate, i.e. to put forward the things which would make the sentence less heavy. Mitigation can be either about the offence or the offender.
^ TOPSides to a story
You might think that the sentence would be the same regardless of the quality of the mitigation, on the basis that the facts of the offence are clear and the situation regarding the offender ought to be reasonably straightforward. It does not work like that. Think of hearing a story told in different ways by two different people. Whilst the basic story might be the same, one might tell it in such a way that you are bored to death listening to it, or even worse irritated by it, and the other might make it interesting. Might make you see things through the eyes of the person they are talking about. If you listen to a good mitigation and a bad one you'll see a huge difference. A good mitigation cannot change everything so that there is an unrealistic sentence, but it can lead to a sentence which is more lenient than would otherwise have been the case.
^ TOPRealistic Plea
One of the most important aspects of the plea in mitigation is that it must be realistic. If someone has been convicted of rape, there might be reasons either as regards the offence which show that this should not be regarded as the most serious offence of its type (whilst any rape is correctly regarded as an extremely serious offence, all other things considered a rape at knifepoint will be regarded as more serious than one not for example and therefore a person guilty of rape without using a knife can expect not receive as long a prison sentence as someone who does). Alternatively there might be facts relating to the offender which might count in his favour. However a plea in mitigation which started in such a case by suggesting that the offender should not be sent to prison at all would (in virtually all circumstances) be so unrealistic that the judge would lose interest in what was being said. The real issue was whether the barrister could get a reduction in the likely length of sentence. If your house is worth £300,000, a tough negotiator might get you down to £275,000, or even £250, 000, but he's never going to get you down to £20,000 and if he started off with that offer you would conclude he wasn't serious. Thus whilst a good plea in mitigation can definitely reduce the sentence, it is only if the person making it is realistic from the start. To paraphrase the old joke, if the barrister mitigating on behalf of someone who has murdered both his parents starts off by asking that the defendant should not be sent to prison because he is only a poor orphan, after that beginning the judge is not really likely to take seriously anything that the barrister says.
^ TOPEffective Difference
Knowing the points to make and the order in which to make them, as well as the language in which to make them, is also critical. You can only work with the material you are given, but it is up to the barrister to make the best of that material. Working out which bits are worth saying and the way to say them. As with all advocacy (performing in court whether making speeches or asking questions of witnesses) it is a question of working out what you can realistically achieve and then the most persuasive way of achieving it. Even in the most difficult of cases, there is usually something which can be said. Even in a dreadful murder, where a life sentence is mandatory, there is still the issue of the minimum recommendation, and if the advocate manages to nudge the judge towards a minimum recommended sentence of 20 years rather than 25 years he has made a very effective difference for his client.