My lawyer tells me that the closing argument is one of the most important parts of a jury trial. Why is that?
The closing argument, also called the summation, is very important because it lets your lawyer put the case together to the jury from the eyes of the defense. Remember the judge gives a speech last. The order of the speeches is defense, prosecution, judge. When the judge speaks last, the attorneys know what the judge is going to say in advance, so if you want to argue any points about the judges speech, you are permitted to make that argument during the closing as well. Trial advocacy is an art, its not a question with an answer. Trial advocacy is a craft the attorney works on their entire career.
The main reason why the closing is so important is because the prosecution has the burden of proof, there are many jury trials where the attorney does not put on any evidence and hardly asks any questions during the case. Further, in the opening statement, the attorney is not allowed to make an argument, just a statement about the facts and the evidence, so the closing in some cases is the first and only time that you can make a real argument about how you see the case.
A good example of this is a date rape case. For this example, the woman tells a friend a month after the incident that her ex-boyfriend came over for dinner and raped her after dinner. There is no other evidence except the testimony of the alleged victim. The criminal defense attorney in that case in their opening statement will say there is no proof his client was ever present for dinner on the night in question, no DNA evidence, no prompt complaint, no medical evidence, and no pictures of injuries to the alleged victim. The defense attorney may ask no questions during the entire case and not call anyone tot he stand. The closing argument will be the only time where the attorney can argue that the alleged victim is a liar, that she made up the whole story because she is angry with the defendant for breaking up with her, etc. The closing argument can be the most important part of your case.