Most criminal cases in the united states are done in a trial by jury. Jury trials are an important part of the justice system .A jury is made up of regular citizens .There are two kinds of juries .a grand jury and a petit jury .A grand jury has between 12 and 23 members. The prosecutor presents his or her evidence to the grand jury. Then, the grand jury decides if there is enough evidence to have a trial .If the jury says yes,then there will be a trial .If the jury says no, there will be no trial . A petit jury is also called a trial jury . This jury has usually 12 members . The members listen to actual court cases .They hear all of the evidence . Then ,at the end of the trial ,they must make a decision .They decide if the defendant is innocent or guilty .